NANOSTRUCTURED COMPOSITES BASED ON POLYELECTROLYTE GELS

Transcription

1 NANOSTRUCTURED COMPOSITES BASED ON POLYELECTROLYTE GELS A.R. Khokhlov *, O.E. Philippova *, S.G. Starodoubtsev, V.V. Vasilevskaya * Physics Department, Moscow State University, Moscow , Russia Nesmeyanov Institute of Organoelement Compounds RAS, ul. Vavilova 28, Moscow , Russia Phone: Fax: khokhlov@polly.phys.msu.ru 1. The results on swelling behavior and the structure of composite gels based on poly(acrylamide), as well as copolymers of acrylamide with cationic monomer units, with incorporated bentonite clay in solutions of sodium chloride and ionic surfactants will be presented [1], [2]. Both the charges of the gel and of the clay play a role of the centers of adsorption of oppositely charged surfactants, cetylpyridinium chloride and sodium dodecylbenzenesulfonate. The Coulombic attraction between the ions of the cationic network and the negative charges of bentonite results in significant shrinking of the gel, which gives rise to amphoteric properties. Both the anionic and cationic surfactants, participate in a competition interaction with the charges of the amphoteric composite and their absorption leads to the marked swelling of the gel. The clay embedded in the gels can be kept in the highly dispersed state after modification with the surfactants while the suspension of the free clay coagulates. The ESR data show that the adsorption of CPC on the clay platelets leads to the formation of ordered surfactant aggregates with low molecular mobility in the region of surfactant concentrations much below the cmc. A SAXS study demonstrates that further adsorption of the surfactant results in the formation of lamellas, including alternating layers of clay platelets and double layers of CPC. These two steps of the adsorption are accompanied by the strong shrinking of the gel composite. At high concentrations of the surfactant, total overcharging of the surface of the clay particles occurs, resulting in a change in the direction of the electroosmotic transport of water through the gel and in the reswelling of the gel composite. The models of the clay/surfactant complexes in the gel phase will be discussed. 2. A new type of intermacromolecular system consisting of a flexible polymer gel with embedded rigid-rod linear polyelectrolyte has been investigated for polyacrylamide hydrogel and linear poly(4,4''-(disodium 2,5-dimethyl-1,1':4',1''-terphenyl-3',2''-disulfonate)). It has been shown that the incorporation of stiff-chain polyelectrolyte inside the uncharged network improves both the ability to absorb water and the mechanical strength of the gel [3]. This makes such systems potentially promising as superabsorbent materials. A surprising effect is that the rods are effectively retained by the gel although they are not covalently attached to the network chains [3]. This is apparently due to the formation of aggregates of rods, which pinch some of the network chains. Self-aggregation of rods was studied by small-angle neutron scattering [4]. It was shown that both inside the hydrogel and in aqueous solution polyelectrolyte rods self-assemble into cylindrical aggregates having eight to nine single polymer chains in the cross-section, the chains being aligned parallel to the axis of the aggregate. The length of these aggregates is much higher than the contour length of a single chain. Gels with embedded rods were studied by contrast variation method in order to examine separately the scattering by the gel and by the rods [4]. Two important observations were made. First, it was shown that the ordering of the rods in the gel resembles that in solution. Second, it was shown that the gel itself is more homogeneous in the presence of rods. Most

2 probably, this effect is due to mobile counterions of rods, which counteract the formation of spatial inhomogeneities in the network during synthesis, because in an inhomogeneous network mobile counterions should be also distributed nonuniformly that is associated with significant translational entropy losses. 3. A simplest theory of swelling of microporous Swiss-cheese polyelectrolyte gels (i.e. polyelectrolyte gels containing regular set of closed water voids) in the solution of 1-1 lowmolecular salt and for the case of multivalent ions solution will be described [5], [6]. It was found that the voids of such gels effectively absorb co-ions. The degree of this absorption increases with the increase of average size of the voids and of their concentration. The theory allows the estimation of the size of water voids starting from which the condition of electroneutrality of water void is fulfilled and concentration of charged co-ions is equal to that in external solution. It was shown that in many cases the effect of concentrating of co-ions in water voids can be observed for water voids of few micrometers or smaller. The multivalent ions within Swiss-cheese gel are distributed inhomogeneously, their concentration within water voids is higher than that in polymer matrix. The degree of ions redistribution is characterised by partition coefficient k (determined as ratio void mat void mat k D = ns ns of the concentrations n s and n s in water void and in polymer matrix correspondingly). It is shown that the partition coefficient k D can be larger than 10 for lowmolecular salt, reaches 10 3 for bivalent ions and is higher than 10 6 for tetravalent ions. In the case of polymer macroions the partition coefficient k D tends to infinity. The ions redistribution within a gel will be preserved when a gel is taken out of solvent. These facts prove that the polyelectrolyte Swisscheese gel can be used as microreactors with well-defined and easily designed form and size, and that such gels can serve as media with extremely inhomogeneous distribution of charged species. The first experimental realizations of this idea will be reported. 1. S.G.Starodoubtsev, N.A.Churochkina, A.R.Khokhlov. Hydrogel Composites of Neutral and Slightly Charged Poly(acrylamide) Gels with Incorporated Bentonite. Interaction with Salt and Ionic Surfactants. Langmuir, 2000, v.16, p S.G. Starodoubtsev, A.A. Ryabova, A.T. Dembo, K.A. Dembo, I.I. Aliev, A.M. Wasserman, A.R. Khokhlov. Composite Gels of Poly(acrylamide) with Incorporated Bentonite. Interaction with Cationic Surfactants. ESR and SAXS Study. Macromolecules, 2002, v.35, p O.E.Philippova, R.Rulkens, B.I.Kovtunenko, S.S.Abramchuk, A.R.Khokhlov, G.Wegner. Polyacrylamide Hydrogels with Trapped Polyelectrolyte Rods. Macromolecules, 1998, v.31, p Yu.D.Zaroslov, V.I.Gordeliy, A.I.Kuklin, A.H.Islamov, O.E.Philippova, A.R.Khokhlov, G.Wegner. Self-Assembly of Polyelectrolyte Rods in Polymer Gel and in Solution: Small-Angle Neutron Scattering Study. Macromolecules, 2002, v.35, pp V.V. Vasilevskaya, A.R. Khokhlov. Swelling and collapse of Swiss-cheese polyelectrolyte gels in salt solutions. Macromol??ul.Theory Simul. 2002, v.11, p V.V. Vasilevskaya, A.A. Aerov, A. R. Khokhlov. Swiss-Cheese Polyelectrolyte Gels as Media with Extremely Inhomogeneous Distribution of Charged Species. Journ.Chem.Phys. (submitted) D

3 Nanostructured Composites Based on Polyelectrolyte Gels Alexei R. Khokhlov Olga E. Philippova Sergei G. Starodubtzev Valentina V. Vasilevskaya Physics Department, Moscow State University, Moscow , Russia

4 Plan of presentation: 1. Self-assembly of polyelectrolyte rods inside the gel matrix. 2. Hydrogels with incorporated clay dispersions 3. Polyelectrolyte gels with embedded voids

5 Self-assembly of polyelectrolyte rods inside the gel matrix

6 Collaborative work Physics Department, Moscow State University, Moscow, Russia Max-Planck-Institut fuer Polymerforschung, Mainz, Germany

7 Polymer gels cross-links polymer chains Gel swollen in a solvent

8 Application of superabsorbent gels personal care products agriculture civil engineering wrapping materials

9 Improvement of gel properties is to reinforce the superabsorbent gel by incorporation of rigid-rod polyelectrolyte inside the gel matrix.

10 Polyelectrolyte rods Water-soluble polyelectrolyte rods were prepared in the laboratory of Prof.G.WEGNER [ CH 3 SO 3 Na + - ] n Sample 1 Degree of polymerization P w =240 CH 3 - SO3 Na + Sample 2 SO 3 Na + [ ] n - Degree of polymerization P w =23

11 Polyelectrolyte rods CH 3 SO3 - Na + Degree of polymerization P w =240 [ ] n CH 3 SO3 - Na + Polyelectrolyte rods contain: hydrophobic rigid poly(p-phenylene) backbone, hydrophilic charged sulfo-groups, which ensure the solubility of the polymer in water. Due to the hydrophobic character of the main chain these polymers undergo self-association in aqueous media.

12 SAXS study of self-aggregation of polyelectrolyte rods Aggregates are of cylindrical shape. Each aggregate contains 3 single polymer chains in a cross-section independently of polymer concentration. Cylindrical aggregates are arranged in a hexagonal lattice. R.Rulkens, G. Wegner, T. Thurn-Albrecht (1999) Langmuir 15, 4022.

13 How the aggregates look like? (crystal structure analysis of model oligomers) Projections of threefold strands along the columnar axis plane normal to columnar axis

14 Preparation of polyacrylamide gel with incorporated polyelectrolyte rods Free-radical copolymerization of acrylamide with cross-linking agent (N,N -methylenebisacrylamide) in aqueous solution of rods As a result of the formation of polyacrylamide network the rods become trapped by the gel.

15 Conditions of preparation of composite gels Gel [monomer], g/l [cross-linker] / [monomer] [rods], g/l PAAm1* 47 1:300 9 PAAm2* 47 1:200 9 PAAm3* 47 1:100 9 PAAm4* 90 1:200 9 PAAm5* 90 1: PAAm1 47 1:300 0 PAAm2 47 1:200 0 PAAm3 47 1:100 0 PAAm4 90 1:200 0 A series of composite gels differing in the cross-linking density, in the concentration of monomer at synthesis and in the content of rods was prepared. The content of rods in the dried gel: 9-18 wt.%.

16 Superabsorbent properties of composite gels Gel PAAm gel without rods PAAm gel with rods Degree of swelling The introduction of polyelectrolyte rods into the uncharged gel improves the ability of the gel to absorb water. This is a consequence of the osmotic pressure exerted by counterions of the rigid-rod polyelectrolyte.

17 Osmotic pressure of counterions of polyelectrolyte rods uncharged network charged rods counterions The counterions cannot escape outside the gel because of the condition of macroscopic electroneutrality. In order to gain in the translational entropy the counterions try to occupy as much volume as possible, thus creating an exerting osmotic pressure.

18 Mechanical properties of composite gels Elasticity modulus G, kpa 2,5 2,0 1,5 1,0 0,5 0,0 PAAm1 (1:300) PAAm2 (1:200) PAAm3 (1:100) with rods without rods Gels with trapped polyelectrolyte rods possess significantly higher moduli of elasticity than the corresponding reference gels without rods.

19 Advantages of composite gels Polyelectrolyte rods impart useful properties to the gel: - higher ability to absorb water, - higher mechanical strength. The counterions of the charged rods are responsible for the enhancement of the absorption capacity of the gel, while the presence of stiff elements in the gel structure gives rise to the increase of the modulus of elasticity. This makes such systems potentially promising as superabsorbent materials.

20 Retention of rods within the gel in water Gel [monomer], g/l [cross-linker] [monomer] Fraction of rods released from the gel [rods in gel] [rods in solution] PAAm1* 47 1: PAAm2* 47 1: PAAm3* 47 1: PAAm4* 90 1: Polyelectrolyte rods are effectively retained by the gel, although they are not covalently attached to the network chains. The release of rods decreases with increasing (1) degree of cross-linking of the network, (2) concentration of monomer (acrylamide) at the gel preparation.

21 Retention of rods within the gel in aqueous salt solution Fraction of PPP3 released by the gel 0,35 0,30 0,25 0,20 0,15 0,10 0,05 gel PAAm2* gel PAAm4* 0,00 0,00 0,02 0,04 0,06 0,08 0,10 Concentration of NaCl, mol/l The low molecular weight salt almost completely suppresses the release of rods from the gel.

22 Polyelectrolyte rods are not linked to the network chains, but... why they are effectively retained by the gel? why they affect the elasticity modulus of the gel? This may be due to the formation of self-aggregates of rods, which jam some of the network chains, because the length of rods (~150 nm) is much higher than the mesh size of the gel (~12 nm).

23 Indications to self-aggregation of rods inside the gel degree of swelling (m-m 0 )/m PAAm-AMPS gel curve corrected for Manning condensation PAAm gel with rods 0 0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 % of charged groups homogeneous distribution of charges PAAm - AMPS gel NH 2 NHC(CH 3 ) 2 CH 2 SO - 3 N ( CH 2 -CH ) n ( CH 2 -CH ) m C=O C=O inhomogeneous distribution of charges PAAm gel with charged rods CH 3 SO 3 - Na + [ ] n H 3 C SO 3 - Na + The degree of swelling of the gel, which «senses» the state of counterions, indicates to self-aggregation of rods inside the gel

24 Release of non-aggregated polyelectrolyte by the gel Percent of linear polyelectrolyte released from the gel 98% 95% 13% Flexible non-aggregated Rigid-rod non-aggregated Rigid-rod aggregated Poly(styrene sulfonate) in water Rods in water/methanol mixture Rods in water Non-aggregated polyelectrolyte is almost completely released from PAAm gel

25 Release of rods from similarly charged polyelectrolyte gel Anionic rods in poly(sodium methacrylate) gel % PPP3 released water 0.01M NaCl 0.05M NaCl 0.5M NaCl time, hrs Rods are completely released from similarly charged gel When electrostatic repulsion is screened by salt, most of the rods are retained by the gel

26 Conclusions Polymer gels with entrapped polyelectrolyte rods were prepared. Polyelectrolyte rods impart useful properties to the gel: - higher ability to absorb water, - higher mechanical strength. Although polyelectrolyte rods are not covalently attached to the network chains, they are effectively retained by the gel. This may be due to the formation of self-aggregates of rods including some of the network chains.

27 SANS study of self-aggregation of rods together with Joint Institute for Nuclear Research, Dubna, Moscow Region, Russia

28 Self-aggregation of rods in solution and inside the gel - SO 3 Na + [ ] n In solution In the gel matrix

29 Polyelectrolyte rods in solution. Form factor. IQ, 10-8 cm wt.% 0.6 wt.% 0.4 wt.% Low concentrations Form-factor of rod-like objects Q 2, A -2 Radius of gyration of the cross-section of rods is 15 Å independently of polymer concentration. This is higher than the radius of single molecule (5 Å). Length of rods is longer than the length of single molecule.

30 Polyelectrolyte rods in solution. Structure factor. S, a.u. 3 C p : -1.0 wt.% -2.0 wt.% -3.0 wt.% -4.0 wt.% High concentrations Q, A -1 Structure peak appears at polymer concentration of ca.1 wt.%. Peak shifts toward higher Q values with increasing polymer concentration

31 Polyelectrolyte rods in solution. Distance between aggregates log(d b ), (d b in A) 2.2 d b ~ C p log(cp), (Cp in wt.%) From the position of peak the interaggregate distance was estimated. The interaggregate distance scales with polymer concentration as d b ~ C p

32 Polyelectrolyte rods in solution. Radial aggregation number a rad From the position of structural peak the radial aggregation number a rad was determined. a rad =9 d b It is independent of polymer concentration. In aqueous solutions rods self-assemble into cylindrical aggregates. Each aggregate contains 9 single polymer chains in a cross-section independently of polymer concentration.

33 Polyelectrolyte rods in the gel matrix

34 Scale of scattering densities D 2 O 80% D 2 O 20% H 2 O cm Scattering densities of the gel and of the rods differ significantly, which allows one to use contrast variation technique. rods matching of rods scattering scattering on the gel 30% D 2 O 70% H 2 O H 2 O gel matching of gel scattering scattering on rods

35 Polyelectrolyte rods in the gel. Scattering from the rods I, cm -1 2 wt.% Solvent: D 2 O/H 2 O (30/70) matching scattering of gel Q, A -1 Self-aggregation of rods inside the gel is the same as in solution: the aggregates are of cylindrical shape each aggregate consists of 8 single chains in the cross-section

36 Effect of salt water 0.2M NaCl IQ, 10-8 cm R 0 = 15 Å IQ, 10-8 cm -2 1E-3 R 0 = 25 Å 1E-3 1E Q 2, Å -2 Q 2, Å -2 Addition of low molecular weight salt leads to: suppression of structure peak, increase of the radius of gyration and of the length of aggregates.

37 Polyelectrolyte rods in the gel. Scattering from the gel I, cm -1 1 gel Solvent: D 2 O/H 2 O (80/20) matching scattering of rods 0.1 gel with rods Q, A -1 The gel is more homogeneous in the presence of rods.

38 Osmotic pressure of counterions of polyelectrolyte rods uncharged network charged rods counterions Mobile counterions of rods counteract the formation of spacial inhomogeneities in the network during synthesis, because in an inhomogeneous network mobile counterions should be distributed nonuniformly that is associated with significant losses of translational entropy.

39 Conclusions Polymer gels with entrapped polyelectrolyte rods were prepared. Polyelectrolyte rods impart useful properties to the gel: - higher ability to absorb water, - higher mechanical strength. Although polyelectrolyte rods are not covalently attached to the network chains, they are effectively retained by the gel. This may be due to the formation of self-aggregates of rods including some of the network chains.

40 Hydrogels with Incorporated Clay Dispersions

41 LIST OF PARTICIPANTS Moscow State University Prof. A.R.Khokhlov, Mrs. A.A.Ryabova Polytechnic of Milan Prof. Giuseppe Allegra, Prof. S.V.Meille, Dr. A.Famulari, Dr. L.Malpezzi. Institute of Crystallography, Russian Academy of Science Dr. A.T.Dembo, Mr. K.A.Dembo Institute of Elementoorganic Compounds, Russian Academy of Science Dr. N.A.Churochkina Institute of Chemical Physics, Russian Academy of Science Prof. A.M.Vasserman, Dr. I.I.Aliev

42 SMALL ANGLE X-RAY SCATTERING 1E-4 1E-5 I, a. u. 1E-6 1E-7 1E q, nm -1 a) The SAXS pattern and the corresponding integrated curve obtained from the composite gel containing 4.0 wt.% BENT at synthesis and treated by 0.01 M solution of hexadecyltrimethylammonium bromide. b) The SAXS profile obtained from the suspension contained 4.0 wt.% of BENT and treated by 0.01 M solution of hexadecylpyridinium chloride (KratkytypeAmur-3K, ICRAS). (Bruker NANOStar diffractometer).

43 CHEMICAL STRUCTURE OF SOME POLYMERS AND IONIC SURFACTANTS USED IN THE STUDY Poly(acrylamide) Poly(diallyldimethylammonium Chloride) (PDADMA) (Strong Polyelectrolytes) CH 2 CH CO NH 2 CH 2 CH CH CH 2 CH CH N Cl CH 3 CH 3 Sodium Dodecyl Sulfate (SDS) SO 3 O Na N Cl Sodium Poly(styrenesulfonate) Sodium Poly(2-acrylamide-2-methyl-1- propanesulfonate) (PAMPS) CH 2 CH SO Na 3 CH 2 CH 3 Cetylpyridinium Chloride (CPC) CH CO HN CH 2 CH CH 2 SO 3 Na

44 THE STRUCTURE OF SODIUM MONTMORILLONITE 1.2 nm 100 nm 1.2 nm THE STRUCTURE OF THE SINGLE PLATELET OF MONTMORILLONITE (MONT). Blue - aluminum-oxygen layer; Purple - silica-oxygen layer; Dotted black - anions of the platelet; Yellow circles - cations (sodium) Composition of MONT-containing clay, bentonite (BENT): Na , Ca , Fe - 1.6, Al , Si wt.%, O - the rest oxygen; 2 - hydroxide; 3 - aluminium, iron or magnesia; 4 - silica or aluminium.

45 THE STRUCTURE OF MONT CRYSTALS AND DISPERSIONS Crystal of montmorillonite in a dry state 300 MONT 5.323, d=1.18 I, a. u BENT 5.04, d= nm 100 nm q, nm -1 WAXS profiles of dry MONT (1) and BENT (2) powders, and aqueous suspensions of MONT (3) and BENT (4) with 4 wt% of the clays. a) b) At low concentration the clay platelets form the card-house structure (a). At higher concentration they tend to have a parallel orientation (b).

46 POLYMER GELS WITH EMBEDDED DISPERSIONS OF CLAYS PREPARATION The gels are prepared by three - dimensional polymerization of monomers in the presence of a suspension of clay particles. The suspension was treated by ultrasound. Polymerizing mixture Suspension THE PARTICLES OF CLAYS EMBEDDED IN THE PAAm GEL DO NOT COAGULATE UNDER THE ACTON OF FLOCULATING AGENTS (Al) 2 (SO 4 ) 3 a) Precipita b) Liquid suspension Composite gel Polymerizing mixture: acrylamide, N,N / -methylene(bis)acrylamide, ammonium persulfate. The addition of (Al) 2 (SO 4 ) 3 leads to fast flocculation of clay suspensions in water (a), while the suspension embedded in the gel (b) remains in the highly dispersed state.

47 POLYMER GELS WITH EMBEDDED DISPERSIONS OF CLAYS 1E-3 1E-4 I, a. u. 1E-5 1E-6 d = 2.0 nm 1 d = 1.34 nm At low concentration the clay platelets form the card-house structure. At higher concentration they tend to have a parallel orientation. 1E-7 1E q, nm -1 SAXS profiles of dry BENT powder (1), dry PAAm-BENT composite (2) and swollen composite gel (3) with 2.4 wt% of BENT. SAXS DATA DEMONSTRRATE THE ABSENCE OF ORDERED STRUCTURES IN THE SWOLLEN GEL-CLAY COMPOSITES UNDER THE STUDY.

48 THE COMPOSITE GELS ARE MATERIALS WITH MEMORY Table 1 Swelling ratios F of the clay-gel composites with different prehistory CLAY, wt. % PAA*, wt. % F 1 F 2 BENT, MONT, MONT, , MONT, MONT, Swollen gel Dried gel *cross-links 1/500 monomer units F 1 gel equlibrated after synthesis in 0.01 M NaCl; F 2 gel after drying and second swelling; F US gel after drying, second swelling and sonication. The drying of the gel composite results in the formation of the new bonds between the clay crystals. Second swelling EFFECT OF MEMORY CAN BE ELIMINATED BY INCREASE OF THE POLYMER CONCENTRATION INTO THE GEL.

49 THE PLATELETS IN THE COMPOSITE GELS INTERACT Time dependence of the swelling ratios F of PAAm - BENT composites CLAY, wt. % PAA*, wt. % BAA/AA F 1 F 2 BENT, / BENT, / F 1 the swelling ratio of the gel equlibrated 7 days after synthesis in water; F 2 the swelling ratio of the gel equlibrated 90 days after synthesis in water. THE GEL - CLAY COMPOSITES ARE RESPONSIVE TO ULTRASOUND drying m=53 mg m=43 mg 51 mg m=1.0 mg sonication The drying of the gel composite results in the formation of the new interactions between the clay crystals. Sonication destroys the new interactions between the clay crystals and the gel remembers its original highly swollen state.

50 THE GELS CONTAINING SUSPENSIONS OF CLAYS DO NOT COLLAPSE IN THE PRESENCE OF ORGANIC SOLVENTS. THEY HAVE A HIGHER MECHANICAL CHARACTERISTICS 100 а) б) 12 Swelling ratio 10 1 Neutral PAAm gel 1. 0% MONT % MONT % MONT Acetone, vol % a) Dependencies of the swelling ratio on acetone content for poly(acrylamide) gel with different content of BENT G, kpa The PAAm gel with (1) and without(2) BENT Acetone, vol. % b) Dependencies of the Young modulus on acetone content for poly(acrylamide) gel with (1) and without (2) 4.0 % of BENT. Applications: super absorbers (hygiene, agriculture...) 1 2

51 GEL-CLAY COMPOSITES DEMONSTRATE POLYELECTROLYTE PROPERTIES DUE TO THE PRESENCE OF NEGATIVE CHARGES ON A SURFACE OF CLAY PARTICLES a) a) Neutral gel containing BENT swells due to additional osmotic pressure created by sodium counterions(yellow circles). b) b) Cationic gel containing BENT shrinks due to electrostatic attraction between the charged groups of the clay (dotted black lines) and of the network (green circles). m sw /m dry E-5 1E-4 1E-3 0,01 0,1 1 C NACL, M Dependencies of the swelling ratio of the gels on the concentration C of sodium chloride for the neutral PAAm gel (1); PAAm-BENT gel (2); anionic (3) and cationic (4) PAAm-BENT gel. Content of AMPS or DADMA groups in the PAAm network 10 mol%.

52 INTERACTION OF MONT AND BENT SUSPENSIONS WITH CATIONIC SURFACTANTS In MONT - type clays bilayers of surfactant alternate with the clay platelets. I, a. u. 10 Q= , q, nm -1 X-ray diffraction profiles obtained from4 wt% suspensions of MONT (1) and BENT (2) treated with 0.1 M cetylpyridinium chloride. (3) - untreated BENT suspension. Calculation for alternating bilayers (Q=2) of surfactant with s=0.25 nm 2 and clay platelets with d=1.25 nm and ρ=2.5*10-6 g/m 3. Platelets surface, S for 1 g (two sides): S=2*((10-6 (m 3 )*10 9 )/(1.25*2.5(m)))=640 m 2 N=640/(0.25*10-18 ); M=N/N A M=4.2*10-3 (mol/g) IS THE SMECTIC-TYPE ORDERING OF THE CLAY PLATELETS POSSIBLE IN THE MATRIX OF CROSS-LINKED GEL?

53 EFFECT OF BENT CONTENT ON THE STRUCTURE OF THE COMPOSITES 20 I, a.u θ, deg THE ABSENCE OF THE ORDERED STRUCTURES IN THE GEL WITH LOW CONTENT OF BENT MANIFESTS THE ABSENCE OF THE AGGREGATION OF CLAY PLATELETS IN THIS CASE. SAXS profiles obtained from the gel-bent composite with 4.0 (1); 2.4 (2) and 1.0 wt% of BENT treated with 0.01 M CPC.

54 ELECTROOSMOTIC TRANSPORT OF WATER IN POLYELECTROLYTE GELS AND GEL - EXPERIMENT Under the action of DC current the release of water from the gel-clay composite (PAAm gel-bent) occurs near cathode. After modification of the gel by the cationic surfactant, CPC water is released near anode. Each elementary charge transport as much as molecules of water. Time of shrinking τ~1/h, where h is the characteristic size of the gel. CLAY COMPOSITES Device artificial hand : MODEL Capillary with the charged walls а) (a) In the PAAm-BENT б) gel water is transported by the cations. (b) In the gel, modified by cationic surfactant water is transported by the anions.

55 SMECTIC ORDERING OF THE PLATELETS IN GEL-BENT COMPOSITES TREATED WITH CATIONIC EXPERIMENT Sealed glass capillary, thickness 1.0 mm Aqueous 0.1 M solution of CPC τ=l 2 /D D 10-5 cm 2 /s The gel I, a.u. 6 4 d, L, nm I, a. u θ, deg SAXS profiles obtained from the composite gel with 4.0 wt% of BENT at different time intervals after mixing with 0.1 M CPC solution t, h After one hour interlamellar distance,d (red), relative intensity (blue), and mean long-range order dimension, L (black) do not change. (Gel with 4% of BENT in 0.1 M CPC.) 0

56 EFFECT OF THE LENGTH OF THE HYDROPHOBIC TAIL OF THE SURFACTANT ON THE SELF ARRANGEMENT OF THE CLAY PLATELETS INTO THE GEL - BENT COMPOSITES. 20 The change in the free energy during the self-ordering of the clay platelets: I, a.u. F= F el + F(N) Stack F el - the change in the elastic free energy; F Stack - the change in the energy of stacking (the energy of hydrophobic interactions) θ, deg SAXS profiles obtained from the gel-bent composite with 2.4 wt% of BENT treated with 0.01 M solutions of hexadecyl- (1), tetradecyl- (2) and dodecyl- (3) trimethylammonium bromides. THE ENERGY OF HYDROPHOBIC INTERACTIONS SHOULD EXCEED THE CRITICAL VALUE: N>N crit

57 Effect of BENT concentration and of the surfactant length* on the position of the maxima, 2θ interlamella distance, d and the mean longrange order dimension L in the swollen gel-clay composites BENT, RN 2θ 1 d1, nm 2θ 1 L, nm wt.% 1.0 R12-R Py R R R Py R R R Surfactants: cetylpyridiniumm chloride (Py16) and alkyltrimethylammonium bromides with alkyl = C12; C14 and C16

58 ABSORPTION OF POSITIVELY CHARGED SURFACTANTS BY GEL-CLAY COMPOSITES [CPC]/[Na + ] I Q=2 II E-5 1E-4 1E-3 0,01 0,1 c, M EXPERIMENT: The surfactant was extracted from the gels by 2 M solution of sodium chloride in 50 vol.% ethanol. Concentration of CPC was measured by spectrophotometry Isotherms of absorption of cetylpyridinium chloride by the PAAm-BENT composite with 2.4% of BENT. Crosslinks - 1/100 (1) and 1/500 (2, 3). 1, 2 - H 2 O, NaCl. The red line shows the amount of the surfactant into the gel corresponding to the idealized smectic crystal. THE COMPOSITE GEL ABSORBS CATIONIC SURFACTANT DUE TO ADSORPTION ON THE PLATELETS (REGION I IN THE FIGURE) AND DUE TO EQUALIZATION OF THE CONCENTRATION OF THE SURFACTANT IN THE SOLUTION AND IN THE GEL (REGION II ).

59 THE STRUCTURAL CHANGES DURING THE ABSORPTION OF CATIONIC SURFACTANT BY THE GEL-BENT COMPOSITE Intensity, a.u. τ = 6.65 H I( + 1) I( 1) ( 1) a) b) sec q, nm -1 a) SAXS profiles of the PAAm-BENT gels modified with cetylpyridinium chloride, CPC. Q - the composition. Q=[CPC]/[CPC theor ]. Q C 15 H 31 2E-9 τ 1E-9 O C 2 H 3 C CH 3 H 3 C CH 3 1 N Intensity O* b) b) I (+1) The spin zond H (+1) a) I (-1) H, Gs 1E-4 1E-3 0,01 0,1 c, M b) Dependencies of the correlation time of the spinprobe in the gels 1/500 and 1/100 on the concentration, c of CPC. In the frame: typical ESR spectrum of the spin-probe in the gel I (c= M)

60 REENTRANT COLLAPSE OF THE GEL-CLAY COMPOSITES DUE TO THE INTERACTION WITH POSITIVELY CHARGED SURFACTANTS Interaction with the cationic surfactant leads to the collapse of the composite gel. However, at high concentration of the surfactant the gel swells again. The mechanism of the contraction and reentrant swelling of the composite gel due to interaction with CPC. I MONT m eq /m dry F I II III I, a. u. Q= Q=12 Q=0.3 II 0 1E-5 1E-4 1E-3 0,01 0,1 c, M Dependences of the swelling ratio of PAAm-MONT gels with the crosslinking degree 1/500 (1) and 1/100 (2) vs. the concentrations of cetylpyridinium chloride. q, nm III MONT

61 GEL-CLAY COMPOSITES MODIFIED WITH CATIONIC SURFACTANTS ABSORB HYDROPHOBIC SUBSTANCES Surface modification of the clay platelets by cationic surfactants makes them hydrophobic. In spite of the hydrophilic nature of the PAA network the composites become capable to absorb hydrocarbons. EFFECT OF THE SURFACTANT STRUCTURE ON THE ABSORPTION OF BENZENE BY GEL-BENT COMPOSITE (PAAm 6.0%, BENT 2.4 %) SURFACTANT Q, vol.% HEXADECYLPYRIDINIUM CHLORIDE 37 HEXADECYLTRIMETHYLAMMONIUM BROMIDE 42 TETRACYLTRIMETHYLAMMONIUM BROMIDE 49 DODECYLTRIMETHYLAMMONIUM BROMIDE 26 I, a.u d=3.9 nm d~4.7 nm Schematic representation of modified MONT structure after absorption of toluene θ, deg SAXS profiles of the PAAm-BENT-CPC gel in a dry state (black) and after swelling in toluene.

62 BEHAVIOR OF THE GEL-CLAY COMPOSITES WITH DIFFERENT CLAYS IN THE PRESENCE OF CATIONIC SURFACTANTS 200 I, a. u MO4A6C initial gel 2 - dry gel 3 - second swelling SAXS profiles of the swollen gel-mont composite, in 0.1 M solution of hexadecyltrimethylammonium bromide (1), after drying (2) and after the second swelling (3). The composition of the gel: MONT - 4.0, PAAm wt %. Cross-links 1/500 monomer units. 0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 q, nm -1 ABILITY OF THE CLAY PLATELETS EMBEDDED IN THE PAAm GELS TO FORM SMECTIC STRUCTURES IN THE PRESENCE OF CATIONIC SURFACTANTS DEPENDS ON THE NATURE OF THE CLAY.

63 SELF ASSEMBLING OF POLYELECTROLYTES AND COLLOIDS ON CHARGED SURFACES PRINCIPLE OF SELF-ASSEMBLING Cations of polymer (protein): Anions of the surface or polymer: Amphoteric protein: Ions of salt: F el a) b) c) F el d) e) F transl 1. THE EFFECT OF THE NETWORK CATIONS ON THE PROPPERTIES OF THE GEL-CLAY COMPOSITES 2. THE EFFECT OF LINEAR CATIONIC POLYMER ON THE PROPERTIES OF THE GEL-CLAY COMPOSITES.

64 COMPETITION BETWEEN THE CHARGES OF THE CLAY AND OF THE NETWORK FOR THE INTERACTIONS WITH THE AGGREGATES OF THE Composite: BENT wt %; acrylamide - 90 wt. %; DADMA - 10 wt. %; Cross-linkes - 1/200 Anionic linear polymer - sodium poly(styrenesulfonate) (PSS); Cationic linear polymer - poly(diallyldimethylammonium chloride (PDADMA). SURFACTANTS 4 Swelling ratio 0 1E-5 1E-4 1E c, M Dependence of the swelling ratio of the cationic composite gel on the concentration of PDADMA (1), PSS (2) and sodium chloride (3) In the cationic gel-bent composite the cations of the network (red) are initially bounded with the anions of the clay plates (black). The clay particles keep the network chains near their surface decreasing the gel swelling. The addition of the charged linear polymer both cationic or anionic leads to the significant swelling of the cationic gel-bent composite PDADMA 2. PSS 3. NaCl 2 1 3

65 COMPETITION BETWEEN THE CHARGES OF THE CLAY AND OF THE NETWORK FOR THE INTERACTIONS WITH THE LINEAR POLYELECTROLYTES The cationic chains of PDADMA have a tenfold higher charge density than the chains of the gel. Therefore, they replace the chains of the network from the surface of the anionic clay platelets and induce the swelling of the gel. Gel chains Anions of the clay Cations of PDADMA Sodium cations Cations of the network Chloride anions Anions of PSS Gel chains Gel chains Gel chains The anionic chains of PSS have a higher charge density than the surface of the clay. Therefore, they form polyelectrolyte complex with the chains of the cationic network, replace network chains of the network from the surface of the anionic clay platelets and induce the swelling of the gel.

66 COMPETITION BETWEEN THE CHARGES OF THE CLAY AND OF THE NETWORK FOR THE INTERACTIONS WITH THE AGGREGATES OF THE Composite: BENT wt %; acrylamide - 90 wt. %; DADMA - 10 wt. %; Cross-linkes - 1/200 Anionic surfactant - sodium dodecylbenzenesulfonate (SDBS); Cationic surfactant - cetylpyridinium chloride (CPC). SURFACTANTS Swelling ratio 0 1E-5 1E-4 1E c, M Dependence of the swelling ratio of the cationic composite gel on the concentration of CPC (1), SDBS (2) and sodium chloride (3) In the cationic gel-bent composite the cations of the network (red) are initially bounded with the anions of the clay plates (black). The clay particles keep the network chains near their surface decreasing the gel swelling. The addition of the charged surfactants both cationic or anionic leads to the significant swelling of the cationic gel-mont composite CPC 2. SDBS 3. NaCl 1 2 3

67 COMPETITION BETWEEN THE CHARGES OF THE CLAY AND OF THE NETWORK FOR THE INTERACTIONS WITH THE AGGREGATES OF THE SURFACTANTS Anions of the clay Cations of CPC Sodium cations Cations of the network Chloride anions Anions of SDBS

68 INTERACTION OF POLYMER PAAm GEL- BENTAY COMPOSITE WITH CATIONIC LINEAR POLYELECTROLYTE (PDADMA) m eq /m dry F 1E-4 1E-3 0,01 0, NaCl I, a. u. 1E-5 1E-6 1E M PDADMA E-4 1E-3 0,01 0,1 С(ПДАДМА), моль/л c PDADMA, M Dependence of the swelling ratio of the gel-bent composite on the concentration of poly(diallyldimethylammonium chloride). BENT wt% E-8 1E q, nm -1 SAXS data (red) shows no order in the arrangement of the clay platelets. 3 The surface of the clay platelets overcharges

69 SELF ASSEMBLING OF POLYELECTROLYTES AND COLLOIDS ON CHARGED SURFACES THE CLAY PARTICLES IN THECOMPOSITE GELS CHANGE THE SIGN OF THEIR CHARGE DURING ALTERNATIVE TREATMANT BY CATIONIC AND ANIONIC POLYELECTROLYTE Swelling Ratio (m/m dry ) a) Anode b) State N/q Cathode Dependencies of the swelling ratio (a) and of the number of water molecules transported by elementary charge N (b) on the state of the surface of PAAm gel-bent composite alternatively treated by PDADMA and PSS. Blue and red arrows - correspond to positively and negatively charged surface in water or (and) 0.01 M sodium chloride.

70 CONCLUSIONS 1. GELS WITH EMBEDDED CLAY SUSPENSIONS ARE MATERIALS WITH MEMORY. 2. IN THE PRESENCE OF CATIONIC SURFACTANTS THE CLAY PLATELETS EMBEDDED IN THE GEL REARRANGE WITH THE FORMATION OF SMECTIC STRUCTURE. 3. THE SURFACE OF THE CLAY PLATELETS CAN BE MODIFIED WITH CATIONIC POLYMERS. 4. THE CATIONIC GELS WITH EMBEDDED CLAY SUSPENSION PROVIDE POLYAMPHOLYTE PROPERTIES.

71 WIDE ANGLE AND SMALL ANGLE X- RAY SCATTERING Wide angle X-ray scattering (WAXS) measurements were performed at the Polytechnic of Milan with a θ/θ diffractometer (ITAL Structures). Small angle X-ray scattering (SAXS) measurements were performed: a) at the Polytechnic of Milan with a Bruker NANOStar diffractometer; b) at the Institute of Crystallography, Russian Academy of Sciences with the Kratky-type (infinitely long slit geometry) Amur 3K diffractometer. In all of the experiments the X-ray wavelength was λ = nm. The scattering vector is defined as q=4π sinθ /λ, where 2θ is the scattering angle. The d-spacing was calculated by the formula: d=2π/q. The mean long-range order dimension L in the gel/surfactant complexes was estimated from the Bragg peaks on the SAXS patterns by the Scherrer formula: L= λ/(β s cos θ.) where β s is the full width at a half-maximum intensity of the peak (in radians) observed at a mean scattering angle of 2θ.

72 Polyelectrolyte gels with embedded voids

73 THEORY Development of the theory of swelling of polymer gels with water-filled voids The theory of swelling and of sorption properties of such gels will be constructed on the basis of the mean field theory of swelling and collapse of a homogeneous polyelectrolyte gel. The formation of the regular structures within the gel with significantly different concentrations of charged species can be analyzed as function of different system parameters, i.e. the degree of polymerization and the degree of ionization of the polymer gel subchains, the size of the water voids, the valence of added ions and their concentration, etc.

74 THREE-DIMENSION POLYMERIZATION IN THE PRESENCE OF SUSPENSION WITH FURTHER DISSOLUTION OF THE SUSPENSION PARTICLES SiO 2 HF Lei Liu, Pusheng Li, Sanford A. Asher. "Entropic trapping of macromolecules by mesoscopic periodic voids in a polymer hydrogel" // Nature, vol 397, 14 January 1999, p

75 L. Liu, P.Li, S. Asher. Entropic trapping macromolecules by mesoscopic periodic voids in a polymer hydrogel. Nature 1999, v.397, p.141 Polyacrylamide gel Sodium polystyrene sulphonate (NaPSS) k HG - partition koefficient between the voids and the gel medium - Polymer of different molecular weight partition between hydrogel matrix and the water voids; - The partition coefficient increases with increase of polymer molecular mass;

76 Donnan effect: еlectroneutrality conditions (for macroscopic systems) + entropic effect

77 «Swiss -Cheese» Polyelectrolyte Gel in 1-1 low-molecular salt void n s R void. - average size of voids; D - average distance between the neighbouring voids D ω = 2 R void 6 π Free energy of voids F void, polymer matrix F mat, external solution F ext 1/ 3 Volume fraction of voids v2 = 1/ω 3 n s n << n mat s s F mat = F el F + void F = int F + F tr en void tr ent + F el st ( F gel + F β void ) = 0; mat ( F + F gel V void ) = F V ext ext ; V.V. Vasilevskaya, A.R. Khokhlov. - Macromolесul.Theory Simul.2002, v.11, p.623 F N mat mat s F = N ext o s ; F N mat mat s F = N void void s

78 Swelling ratio α as function of concentration of salt in the solution 10 r=45, ω=4, χ=0 M=1 f=1 P=100 Q= α F=m eq /m dry 6 Q=4 F α x ext Φ p Theory 0 1E-5 1E-4 1E-3 0,01 0,1 1 c, M Experiment Dependence of the swelling ratio F of gels obtained in solution (1) in the presence of anionic micelles (2) and oil droplets stabilized with anionic surfactant (3) on concentration of NaCl. 5 mol % of cationic groups

79 Concentration of salt in voids n s void as function of the void size R void n s void /n s 1,0 0,8 0,6 a b 0,4 n s =10-4 (a), 10-6 (b) 0,2 0,0 R void, 0 /d The monomer size d ~ 1 nm, is the radius of water void R voido, starting from which salt concentration within water voids is approximately equal to that in external solution, is about 500 nanometers or 5 µm,correspondingly. In the general case, characteristic radius can vary from few nanometers to few micrometers.

80 EFFECT OF SALT CONCENTRATION IN THE SOLUTION ON DISTRIBUTION OF MULTIVALENT CATIONS BETWEEN VOIDS AND POLYMER MATRIX d 10 5 c k D = C void /C sol k D b a z= 1(a), 2(b), 3(c), 4(d) n s Partition coefficient k D as a function of concentration n s for different valences z: 1 (a), 2 (b), 3 (c), 4 (d). χ=0

81 Conclusion The simplest theory of Swiss-cheese polyelectrolyte gel is proposed. It was found that the voids of such gels effectively absorb co-ions. Therefore, the distribution of co-ions within the gel is highly inhomogeneous. It was shown that in the case of macroscopic water voids, the concentration of co-ions within voids is always higher than that in polymer matrix and can be equal to that in external solution. Our theory allows to estimate the size of water voids starting from which the condition of electroneutrality of water void is fulfilled and concentration of charged co-ions is equal to that in external solution. It was shown that in many cases the effect of concentrating of co-ions in water voids can be observed for water voids of few micrometers or smaller. This fact allows to propose that the polyelectrolyte Swiss-cheese gel could be used as microreactors with well-defined and easily designed form and size. A.A.Aerov, V.Vasilevskaya, A.R. Khokhlov, in press

82 THREE-DIMENSION POLYMERIZATION IN THE PRESENCE OF EMULSION WITH FURTHER DISSOLUTION OF THE EMULSION PARTICLES Voids Oil-in Water Emulsion Stabilized with Ionic Surfactant. Emulsion Droplets Immobilized In the Cross-Linked Gel Oil is a mixture of benzene with cyclohexilbromide The Gel Structure after th Removal of Oil Droplets.

83 CHEMICAL STRUCTURE OF MONOMERS AND SURFACTANTS USED IN THE STUDY (3-acrylamidopropyl)trimethylammonium chloride (APTAC) -CH 2 -CH- eutral matrix: oly(acrylamide) (PAA) cross-linked with,n / -methylene(bis)acrylamide (BAA) harged monomer units: odium 2-acrylamide-2-methyl- C = O NH CH 2 CH 2 CH 2 NCH3) + 3 Cl - -propanesulfonate (AMPS) inear Polyanions: oly(amps), Poly(acrylamide-co-AMPS) Surfactants Sodium dodecyl sulfate (SDS) (or sodium dodecyl benzenesulfonate, (SDBS)) (Strong Polyelectrolytes)

84 OPTICAL MICROSCOPY a) b) Poly(acrylamide) gels with included emulsions of benzene prepared at concentrations of SDS of 1.8*10-3 (a) and 2.0*10-4 (b) M.

85 Size distribution of benzene droplets obtained by optical microscopy

86 GEL FORMATION PRACTICALLY DOES NOT AFFECT THE SIZE AND THE SIZE DISTRIBUTION OF THE EMULSION DROPLETS d mean = 2,24±0.48 µ Emulsion in water (25 vol. % of oil) d, mk Size distribution of emulsion droplets in the emulsion d mean = 2,39 ± 0.62 µ 20 Emulsion in gel (25 vol. % of oil) d, mk Size distribution of pores in the gel

87 DISTRIBUTION OF MODEL IONS BETWEEN ANIONIC GEL AND SOLUTION Gel body Concentration of dye in solution C out Anions of the gel, C a >C out Counter ions of the gel and dye, C~C a >> C out Anions of the dyes, C gb <C out Void Average concentration of the dye in the gel, C dye C dye ~C gb *v gb + C void *v void C gb and C void concentrations in the gel body and in the voids; v gb and v void volume fractions of the gel body and voids respectively. (0.75 and 0.25) SO Na 3 SO Na 3 NH 2 NH O C Hydrotype Yellow (Z=4) Bromophenol Blue (Z=2 at ph>4) NH 2 NH SO Na 3 SO Na 3 For the large voids C void ~ C out

88 ABSORPTION OF DYES BY THE GELS WITH AND WITHOUT VOIDS C gel, M 1x10-4 1x10-5 C gel ~C gb *v gb + C void *v void C gel = 0.75 C gb C sol Calculated (squares) and experimental (circles) values of dye concentration in the gel with voids coincide C sol, M Plot of average concentration in the gel with (circles) and without (triangles) voids on concentration of bromophenol blue in water.

89 ABSORPTION OF DYES BY THE GELS WITH AND WITHOUT VOIDS 1x10-4 C gel ~C gb *v gb + C void *v void C gel = 0.75 C gb C sol C gel, M 1x10-5 GEL WITHOUT VOIDS GEL WITH VOIDS CALCULATED VALUES OF C GEL FOR THE GEL WITH VOIDS Calculated (squares) and experimental (circles) values of dye concentration in the gel with voids coincide C sol, M Plot of average concentration in the gel with (circles) and without (triangles) voids on concentration of hydrotype yellow in water.

90 EFFECT OF SALT CONCENTRATION IN THE SOLUTION ON THE AVERAGE CONCENTRATION OF THE CO-IONS IN THE GEL WITH VOIDS n s net c b a R void,0 /d =10(a), 45(b), 1000(c) n s Average concentration of multivalent co-ions within Swiss-cheese gel as a function of external concentration n s for = 4, z = 2 and different values of water voids radius : 10 (a), 45 (b), 1000 (c). Dashed line shows the corresponding dependence for homogeneous gel.

91 DETERMINATION OF DIFFUSION COEFFICIENTS OF THE DYES D τ /D τ 1/2 α D diff 2 Lπ D = 16τ D 4 tgα = L π 2 D diff L D diff - diffusion coefficient; L - thickness of the gel film at τ τ - time of colouring; D - optical density of the film at t = τ; D - final optical density of the film.

92 DIFFUSION COEFFICIENTS OF THE DYES WEAKLY DEPEND ON THE PRESENCE OF VOIDS IN THE GELS 1.0 D t /D inf t 1/2,sek 1/2 D void =(4.0±0,3) м²/s D hom = (3.7 ±0,3 ) м²/s 1.0 D t /D inf t 1/2,sek 1/2 Hydrotype Yellow 104 D void =(4.1±0,3) м²/s

93 Swiss-cheese gels in solution of polyelectrolyte 0,4 k D -1 f p = 0.1(a), 0.2 (b) 0,2 a 0,0 b M Partition coefficient k D as a function of polyelectrolyte degree of polymerization M for R void /d = 10000, = 4 and different values of polyelectrolyte degree of ionization f p : 0.1 (a), 0.2 (b).

94 PENETRATION OF ANIONIC POLYELECTROLYTE Labels (n=3): A. Staxanov, INEOC RAS Labeled Copolymers (yellow): N.Churochkina, INEOS RAS AND SURFACTANT IN ANIONIC GEL. Anionic dyes; Anionic micelles of SDBS with solubilized Sudan-3 dye; Linear labeled polyanions of PAMPS. ELECTROPHORESIS STUDY Gel NaCl, 80 v, 1.5 ma RESULTS: 1. Electrophoretic mobility of anionic Dyes is 2-3-fold lower in comparison with neutral gel. 2. The micelles of anionic surfactant, SDBS loose solubilized hydrophobic dye, Sudan-3 on the surface of the anionic gel (5% of AMPS). 2. Polyanions with mol.% of AMPS do not penetrate in the anionic gel. Sudan-3 PAMPS R CH 2 = C - COO - (CH 2 ) n - O N = N CN

95 COLLAPSE AND SWELLING OF POLYELECTROLYTE GELS WITH (1) AND WITHOUT (2) VOIDS F=m(t)/m eq F=m(t)/m eq 1,0 1,0 0,8 gel without voids gel with voids 0,8 F 0,6 0,4 F 0,6 0,4 gel without voids gel with voids 0,2 0,2 0, t 1/2,min 1/2 0, t 1/2,min 1/2 Experiment: 20 0 C, 50% ethanol, films thickness 2,4 mm, mixing. On the early stages the collapse and the swelling of the samples do not depend on the presence of voids. Voids are isolated.

96 COPOLYMERIZATION OF CHARGED AND NEUTRAL MONOMERS IN SOLUTION, IN THE PRESENCE OF MICELLES AND EMULSION DROPLETS STABILIZED WITH IONIC SURFACTANT a) b) c) Charged monomer open circle, neutral monomer closed circle 40 nm - CH 2 - CH - 1 µ C = O NH CH 2 CH 2 CH 2 NCH3) + 3 Cl - APTAC 10 mol % a) Due to close reactivity of AAm and APTAC in radical copolymerization and high ionic strength in the solution distribution of the charges along polymer chains is random. b) Cations of APTAC concentrate near anionic surface of micelles. Cations form sequences with enhanced charge density. c) The surface of oil droplets is covered by anionic surfactant. Cations of APTAC concentrate near anionic surface of droplets and form sequences with enhanced charge density after copolymerization.

97 SWELLING BEHAVIOR AND ABSORPTION PROPERTIES OF CATIONIC GELS OBTAINED IN SOLUTION (1), IN THE PRESENCE OF MICELLES (2) AND EMULSION DROPLETS STABILIZED WITH ANIONIC SURFACTANT (3) Q=[SDBS - ]g/[-nr 3+ ]g 0,5 0,4 2, 3 Q 0,3 0,2 0,1 1 0,0 5,0x10-5 1,0x10-4 1,5x10-4 2,0x10-4 2,5x10-4 c, M MICROGRAPH OBTAINED FROM THE CATIONIC GEL AFTER POLYMERIZATION IN THE PRESENCE OF OIL-IN-WATER EMULSION DEPENDENCE OF THE CHARGE RATIO Q OF THE GELS OBTAINED IN THE SOLUTION (1), IN THE PRESENCE OF ANIONIC MICELLES (2) AND OIL DROPLETS STABILIZED WITH ANIONIC SURFACTANT (3) ON THE CONCENTRATION OF SDBS.

98 CONCLUSIONS 1. The theory of behavior of polyelectrolyte gels with incorporated voids predict that the concentration of co-ions in the charged gels is significantly decreased in comparison with their concentration in the voids. The effect of the gel structure and the charge of the ions is analyzed. 2. Polyelectrolyte gels with embedded voids can be obtained via three dimension polymerization in the presence of oil in water emulsion. The size distribution of the voids can be regulated by changing surfactant concentration during emulsion preparation. 3. The ions having the same sign of the charge as a gel are concentrated in the voids, while in the gel body their concentration is significantly lowered. 4. Linear polyelectrolytes and micelles do not penetrate in the charged gel of the like charge. 5. Polyelectrolyte gels containing the voids with charged walls are synthesized. They have enhanced ability to absorb oppositely charged surfactants.

99 INTAS New Generation of Smart Polymers and Polymeric Materials for Biotechnology Swiss-cheese polyelectrolyte hydrogels. Valentina Vasilevskaya Artem Aerov Alexei Khokhlov Moscow, May, 2003

100 Task 5. Development of the theory of swelling of polymer gels with water-filled voids The theory of swelling and of sorption properties of such gels will be constructed on the basis of the mean field theory of swelling and collapse of a homogeneous polyelectrolyte gel. The formation of the regular structures within the gel with significantly different concentrations of charged species can be analyzed as function of different system parameters, i.e. the degree of polymerization and the degree of ionization of the polymer gel subchains, the size of the water voids, the valence of added ions and their concentration, etc.

101 L. Liu, P.Li, S. Asher. Entropic trapping macromolecules by mesoscopic periodic voids in a polymer hydrogel. Nature 1999, v.397, p.141 Polyacrylamide gel Sodium polystyrene sulphonate (NaPSS) k HG - partition koefficient between the voids and the gel medium - Polymer of different molecular weight partition between hydrogel matrix and the water voids; - The partition coefficient increases with increase of polymer molecular mass;

102 Swiss-cheese gels as a set of mictoreactors.

103 Collapse of polyelectrolyte gels Jump -wise collapse transition due to osmotic pressure of counterions Polyelectrolyte gels = responsive gels T. Tanaka. Collapse of gels and critical endpoint. Phys.Rev.Lett. 1978, v.40, p. 820

104 Polyelectrolyte gels in low-molecular salt solution in P ~ ( n s n out s ) Experimental data V.V.Vasilevskaya, A.R. Khokhlov Ohmine, T. Tanaka. Salt effects on the phase transitions of ic gels. J.Chem.Phys. 1982, v.77, p.5725

105 in alt concentration n s within polyelectrolyte gel as function of solvent quality x out n s swollen gel V.V.Vasilevskaya, A.R. Khokhlov collapsed gel n n n in s in s in s < n n << out s out s n out s n /σ ~ for swollen gel for collapsed gel in n s Concentration of salt within gel is always lower than that in extertnal solution out n s

106 Donnan effect: еlectroneutrality conditions (for macroscopic systems) + entropic effect membrane

107 «Swiss -Cheese» Polyelectrolyte Gel in 1-1 low-molecular salt void n s R void. - average size of voids; D - average distance between the neighbouring voids D ω = 2 R void 6 π 1/ 3 Free energy of voids F void, polymer matrix F mat, external solution F ext n s n << n mat s s F mat = F el F + void F = int F + F tr en void tr ent + F el st ( F gel + F β void ) = 0; mat ( F + F gel V void ) = F V ext ext ; F N mat mat s = F N ext o s ; F N mat mat s = F N void void s V.V. Vasilevskaya, A.R. Khokhlov. - Macromolесul.Theory Simul.2002, v.11, p.623

108 Concentration of salt in voids n s void and in polymer matrix n s mat n s = 10-3 (a), 10-4 (b), 10-5 (c). a',b' n mat 10 0 s /n s void n s ns mat n s ns n n c' a mat s void s n s n s - solid curves - dash curves 10-3 b c χ -1,0-0,5 0,0 0,5 1,0 1,5 2,0

109 Concentration of salt in voids n s void as function of the void size R void n s void /n s 1,0 0,8 0,6 a b 0,4 n s =10-4 (a), 10-6 (b) 0,2 0,0 R void, 0 /d he monomer size d ~ 1 nm, then the radius of water void R voido, starting from which the salt concentratio ithin water voids is approximately equal to that in external solution, s about 500 nanometers or 5 µm, correspondingly. In the general case, characteristic radius can vary from few nanometers to few micrometers.

110 Swiss -Cheese Polyelectrolyte Gel in Multivalent Salt and Polymer Solutions Q - valency of ion

111 φ void P φ mat P as function of concentration ext φ p 10 7 R void /d=45, ω=4, χ=0, M=1 f=1 P= Q=4 Φ p void /Φp mat Q=3 Q=2 Q= x ext Φ p

112 Swelling ratio α as function of concentration ext φ p 10 r=45, ω=4, χ=0 M=1 f=1 P=100 Q=1 8 6 Q=4 α 4 2 1x ext Φ p

113 void φ P φ ext p as function of pore size R. ω=4, χ=0 Q=1,2,3,4 f=1, P=100, φ p ext =10-5 1,0 0,8 Q=4 Q=1 φ P void /φp ext 0,6 0,4 0,2 0,0 R/d

114 void φ P φ mat P as function of pore size R Q=4,3,2,1 χ=0, P=100, w=4, φ p ext =10-5 Q=4 Q=3 φ p void /φp mat Q=2 Q= R/d

115 Fraction of counterions in pore as function of pore radius R β 8,0x10-3 Q=4,3,2,1 χ=0, P=100, ω=4, φ ext =10-5 p 6,0x10-3 β 4,0x10-3 2,0x R void 0 /d

116 Swiss-cheese gels in solution of polyelectrolyte M - degree of polymerization; f p - degree of ionization