2.1 Traditional and modern applications of polymers. Soft and light materials good heat and electrical insulators

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1 . Polymers.1. Traditional and modern applications.. From chemistry to statistical description.3. Polymer solutions and polymer blends.4. Amorphous polymers.5. The glass transition.6. Crystalline polymers.7. Polymer networks.8. Polymer nanocomposites 1

2 .1 Traditional and modern applications of polymers Traditional applications problem: waste / recycling ENTROPY!!! Soft and light materials good heat and electrical insulators

Block copolymer thin films as gas sensors Jung,

mask consisting of cylinder-forming diblock

3 Block copolymer thin films as gas sensors Jung, Ross et al., Nano Letters 8, 3776 (008) array of well-ordered conducting polymer nanowires etch mask consisting of cylinder-forming diblock copolymers wires act as sensor for ethanol vapor high degree of order achieved by treatment with toluene vapor 3

4 Drug delivery from nanogels M.D. Blanco et al., Polymers 3, 1107 (011) thermoresponsive nanogels diameter 600 nm release of cancer drug 5-Fluorouracil poly[(p-nitrophenyl acrylate) -co-(n-isopropylacrylamide)] cumulative amount of 5-FU released from nanogels Nanostructured polymer particles for enhanced drug uptake in the cell 4

5 Controllable ultrafiltration A. Nykänen, Macromolecules 007 coating with switchable P(S-b-NIPAM-b-S) poly(styrene-b-nipam-b-styrene) 118 kg/mol, f PNIPAM = 0.77 conventional filter permeable only für small molecules permeability decreases strongly upon collapse 5

consisting of a LARGE number (N) of monomers (= repeat units) monomer

6 .. From chemistry to statistical description chemical connection of a large number of monomers Polymers are chain-like macromolecules consisting of a LARGE number (N) of monomers (= repeat units) monomer styrene polymer polystyrene degree of polymerization N: number of polymerized monomers 6

7 Degree of polymerization N may be very high solid materials (entanglements) description by statistical means 7

8 A few polymers polypropylene plastic bags poly(1,4-butadiene) rubber tires poly(dimethylsiloxane) silicone poly(ethylene oxide) PEG poly(p-phenylene-terephthalamide) Kevlar 8

9 The radius of gyration characteristic size of a single polymer characteristic length scales / sizes: mean-square end-to-end distance R 1/ R g radius of gyration ur ur R R R g 1 N i cm N i = 1 ( ) R R ur i : monomer position calculation in lecture R ur cm : polymer s center of mass 9

10 A close look at the chain bond vector r i between atoms C i-1, C r i = axis of rotation for r i + 1 bond angle θ i constant 10

11 Various single chain models ideal chain model: no interactions between monomers rotations around bonds unhindered bond length and angle fixed r Rg = 1 nl 6 n: number of monomers l: monomer length freely rotating chain: 1. all bond lengths b and angles θ fixed. all rotation angles ϕ equally probable r R g 1 = nl 6 1+ cosθ 1 cosθ hindered rotation model: 1. all bond lengths and angles fixed. potential of rotation not constant r R g 1 = nl 6 1+ cosθ 1+ 1 cosθ 1 cosϕ cosϕ 11

12 The characteristic ratio C all corrections are comprised in C r 1 = nl C 6 R g e.g. for hindered rotation model C = 1+ cosθ 1+ 1 cosθ 1 cosϕ cosϕ C is found in tables for all common polymers polymer C b (Å) b: Kuhn segment length 1,4-polybutadiene polypropylene poly(dimethylsiloxane) polyethylene atactic polystyrene

13 Coarse-graining: The equivalent freely jointed chain true chain: n monomers of length l equivalent chain: N monomers of length b Kuhn monomers (i) contour length: Nb = R max (ii) end-to-end distance: R = N b = C n l N = b = R C max nl C nl R max 0 1/ R = R = b N coarse-grained chain with b, N follows simple scaling law 13

14 Free energy of an ideal chain force needed to pull on a chain Helmholtz free energy ur U( N, R ) = 0 F = U - TS no interactions F = TS ur ur entropy S( N, R) = k ln Ω( N, R) B Ω( N, R) ur : number of conformations of freely jointed chain of N monomers with end-to-end vector R ur Gaussian distribution of end-to-end vectors ur ur 3 R F( N, R) = k (,0) B T + F N Nb free energy of a single chain having an end-to-end-vector R ur 14

15 elastic force when separating the chain ends by R x in x direction ur F( N, R) 3k fx = B T = R R x Nb x r 3k B T ur the lower T, f = R Nb elastic spring constant the lower the spring constant, the softer the chain force ~ elongation: looks like Hookes law but origin is different from normal spring: solid: enlargened distance between atoms polymer: unfolding of bonds entropic elasticity origin of rubber elasticity chain = entropy spring 15

16 .3. Polymer solutions Solvent quality: interaction monomer solvent good solvent: maximization of monomer-solvent contacts chain expansion, swollen chain 1/ R g ~ ν N ν = /5 theta solvent: balanced interactions unperturbed (ideal) chain r R g 1/ ν = 1/ = N 1/ bc 6 1/ 1/ poor solvent: minimization of monomer-solvent contact chain collapse, clustering, precipitation 16

H-bonds with adjacent amide group zipper effect swollen collapsed cloud point

17 Transition good solvent poor solvent Poly(N-isopropylacrylamide) (PNIPAM) in water below cloud point H-bonds with H O (cage structure) above cloud point H-bonds with adjacent amide group zipper effect swollen collapsed cloud point T T < 3 C T > 3 C H O is H O is good solvent poor solvent cloud point = 3 C 17

18 Good solvent theta solvent from Rubinstein, Colby. Data compiled by L.J. Fetters, J. Phys. Chem polystyrene in benzene (good solvent) 1/ R g ~ N 0.59 polystyrene in cyclohexane (theta solvent) R g 1/ ~ N 0.50 The swelling of the chain in good solvent results as a balance of the repulsion energy between monomers and the entropy loss due to increased end-to-end vector 18

19 Concentration regimes in polymer solutions if intermolecular bonds present (e.g. hydrogen bonds, vulcanization) gelation from concentrated solution c < c* c c* c > c* dilute solution characteristic lengthscale: Rg N 3 / 5 semidilute chains start to overlap concentrated solution characteristic lengthscale: mesh size ξ 19

20 Phase behavior of polymer solutions From Rubinstein, Colby: Polymer Physics. Data from N. Takano et al., Polym. J φ 1φ φ 1φ g/mol g/mol φ A polyisoprene solutions in dioxane: for g/mol at C: miscibility only for φ < ~0.0 and φ > 0.0 for g/mol at C: miscibility for all φ first-order phase transition from 1-phase to -phase system transition temperature depends on polymer molar mass and on polymer volume fraction φ A : volume fraction of polymer in solvent c vmonn φa = = c ρ M mon Av c: polymer concentration ρ: polymer mass density v mon : monomer volume M mon : monomer molar mass 0 N Av : Avogadro s constant

Chap. 2. Polymers Introduction. - Polymers: synthetic materials <--> natural materials

Chap. 2. Polymers Introduction. - Polymers: synthetic materials <--> natural materials Chap. 2. Polymers 2.1. Introduction - Polymers: synthetic materials natural materials no gas phase, not simple liquid (much more viscous), not perfectly crystalline, etc 2.3. Polymer Chain Conformation