Plasma functionalization of nano- and micro-sized particles

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1 Engineering Conferences International ECI Digital Archives Design and Manufacture of Functional Microcapsules and Engineered Products Proceedings Plasma functionalization of nano- and micro-sized particles James W. Bradley University of Liverpool, UK, Follow this and additional works at: Recommended Citation James W. Bradley, "Plasma functionalization of nano- and micro-sized particles" in "Design and Manufacture of Functional Microcapsules and Engineered Products", Chair: Simon Biggs, University of Queensland (Aus) Co-Chairs: Olivier Cayre, University of Leeds, UK Orlin D. Velev, North Carolina State University, USA Eds, ECI Symposium Series, (2016). microcapsules/6 This Abstract and Presentation is brought to you for free and open access by the Proceedings at ECI Digital Archives. It has been accepted for inclusion in Design and Manufacture of Functional Microcapsules and Engineered Products by an authorized administrator of ECI Digital Archives. For more information, please contact

2 Plasma functionalization of nano- and micro-sized particles James W Bradley Department of Electrical Engineering and Electronics, Brownlow Hill, Liverpool, L69 3GJ, UK j.w.bradley@liv.ac.uk

3 Technological Plasma Group, EEE, UoL The group has a Research Fellow, a lab technician and 3 post docs and 16 PhD students Bradley Bowden Walsh Tu McKay Bryant Physical Vapour Deposition of functional thin films/coatings (magnetron sputtering) Low-pressure plasma surface modification and polymerisation Last 5 years has topped 6M We have 5 laboratories, one with five researchscale industrial systems and a laser and complex plasma laboratory - 0.6M Atmospheric-pressure plasmas functional film deposition and treatment, decontamination, sterilization and catalysis

equilibrium kt e >> kt i kt gas kt surface Incident particle Plasma treatment

4 Plasma Environment A cocktail of positive and negative ions, electrons, radicals, metastables and photons (UV-visible) Plasma constituents: Non- thermal equilibrium kt e >> kt i kt gas kt surface Incident particle Plasma treatment Sputtered particle Remove material Atomic collisions Add material Chemical / physical changes

Advantages of plasma functionalization Clean, low cost, environmentally friendly, efficient, large range of precursors, pin-hole free, complex geometry, large range of target materials including

5 Advantages of plasma functionalization Clean, low cost, environmentally friendly, efficient, large range of precursors, pin-hole free, complex geometry, large range of target materials including particulates, multitude of applications. Surface modification of 2-D surfaces studied extensively in last 25 years Functionalization of micro and nano-particles Low pressure RF plasma reactor The use of nano-particles in modern engineering and healthcare is rapidly growing. Applications in drug release, diagnostics, environmental (oil) clean-up, photovoltaics, advanced coatings, catalysis.etc.. Retain bulk properties (strength, melting point, density, (non) toxicity, solubility) Impart new functionality to the surface, define topology and chemical functionality. The surface chemistry mirrors the starting monomer - functional retention

Low-pressure plasma polymerization on 2-D and

Acrylic acid, NIPAAm, Hexane, Allylamine,

. Functional retention Key metric: Power/flow

6 Low-pressure plasma polymerization on 2-D and 3-D structures Pulsed Capacitive (0-50 W) and Inductively coupled ( W) RF (13.56 MHz) sources 3D porous PLA Scaffolds Acrylic acid, NIPAAm, Hexane, Allylamine, Heptylamine.. Functional retention Key metric: Power/flow rate: 1 W/sccm = 15.5 ev/molecules S Voronin et al J. Vac. Sci. Technol. A 254 (2007) 1093

Plasma treatment - Surface conditioning of plastic electronics 2-step in-situ process works on the patterned samples 300 s O 2 plasma + 30 s CF 4 plasma O 2 plasma treatment, 1 W CF 4 plasma

7 Plasma treatment - Surface conditioning of plastic electronics 2-step in-situ process works on the patterned samples 300 s O 2 plasma + 30 s CF 4 plasma O 2 plasma treatment, 1 W CF 4 plasma treatment, 1 W contact angle (deg) % ZPN 100 % ITO treatment time (s) contact angle (deg) % ZPN due to polymer-like contamination (PDMS, etc) (?) 100 % ITO treatment time (s) O 2 plasma followed by CF 4 plasma works: CF 4 plasma followed by O 2, it does not work

8 Plasma modification of particulates

plasma gases NH 3 Effectiveness: HCOOH < H 2 O < CO 2 < O 2 V Bruser et al,

9 How to handle nano and micro particles? Vibrating bed or a rotary drum NH 3, HCOOH, H 2 O, CO 2 and O 2 used as plasma gases NH 3 Effectiveness: HCOOH < H 2 O < CO 2 < O 2 V Bruser et al, Surface modification of carbon nanofibres in low temperature plasmas, Diamond and Related Materials 13 (2004) 1177

10 Purpose built rig for polymerization and treatment of nano and micro-particles

Up to 100 W RF Typical running pressures 10-100 mtorr Flow rates 1-10 sccm Vibrating bed -

1 mtorr Run times 10-300 s Typical deposition rates (2-D) - a few 50-100 nm/min Run in pure

11 Up to 100 W RF Typical running pressures mtorr Flow rates 1-10 sccm Vibrating bed - 40 Hz Base pressures < 0.1 mtorr Run times s Typical deposition rates (2-D) - a few nm/min Run in pure monomers: Acrylic acid and allylamine Gases: O 2, H 2, air Trials with polystyrene spheres, carbon-based nano-particles and porous silicon-based microparticles

12 Plasma particle interaction in vacuum polymerization M R * R * R * MH + - R * Particle e - fast e - slow R * M R * 2MH + M-X +

13 PS nano-particle plasma treatment Application: Loading solid drug nanoparticles into a gel and monitoring the release of free drug from the gel. Using inert PS spheres as a model of solid drug nanoparticles in gels. Dr Tom McDonald, Dept. of Chemistry, University of Liverpool Video of lycopodium powder shaking

PS nano-particle treatment Oxygen O₂ Acrylic acid CH₂=CHCO₂H Allylamine CH₂=CHCH₂NH₂ Quality Check Before freeze drying particles were analysed with DLS and SEM to check quality of sample.

14 PS nano-particle treatment Oxygen O₂ Acrylic acid CH₂=CHCO₂H Allylamine CH₂=CHCH₂NH₂ Quality Check Before freeze drying particles were analysed with DLS and SEM to check quality of sample. Particle Z - Average Diameter: 830nm +/- 5nm Polydispersity Index (PdI): Adam Town, PhD Student, McDonald Group, Department of Chemistry, University of Liverpool A.R.Town@liv.ac.uk

15 Results Some selected data Acrylic acid polymerization 20 W, 50 mtorr T1-2 mins T2-5 mins

Results Dispersion Process - Samples dispersed on a ball mill for 30 minutes - conc. of 1 mg/ml. Samples diluted to 0.1 mg/ml in distilled water, 25 o C, ph =10.3 with NaOH.

16 Results Dispersion Process - Samples dispersed on a ball mill for 30 minutes - conc. of 1 mg/ml. Samples diluted to 0.1 mg/ml in distilled water, 25 o C, ph =10.3 with NaOH. Zeta Potential - Malvern Zetasizer Nano (Laser Doppler Electophoresis) * The acrylic acid coatings has increased the negative zeta potential of the particles. Hydrodynamic Diameter - Malvern Zetasizer Nano (DLS) * Correlogram plots and PdI values imply the coating has helped the particles fully disperse into solution. T2 (5 mins) has negligible aggregates present. T1 (2 mins) has a small amount of aggregated material (increased hydrodynamic diameter).

17 Results Some selected data Allylamine polymerization 20 W, 50 mtorr, 2 mins

18 Dispersion Process Samples were diluted to 0.1 mg/ml and adjusted to correct ph10 with NaOH or HCl. Zeta Potential *At ph2.8 the stabiliser charge (PAA) is switched off. With increasing ph the zeta potential increases as the allylamine charge diminishes at the expense of PAA. At ph3.0 +/- 0.5 allylamine coated particles are more positive 0.8-(-)13.7 = +14.5mV Hydrodynamic Diameter *Allylamine coated PS particles at ph2.8 aggregate more: Positive allylamine neutralises the KPS initiator negative charge, removing electrostatic colloidal stability. At ph9.7 the correlogram and PdI imply aggregation of 1 m particles ~ 100 m size.

19 Name Pos FWHM Area At% : wide Binding Energy (ev) Name Pos FWHM Area At% wide Binding Energy (ev) Name N 1s S 2p Pos FWHM Area At% wide Binding Energy (ev) Name S 2p Si 2p Pos FWHM Area At% wide Binding Energy (ev) S 2p S 2p CPS Variable 3 Name 1s 1s FWHM Area At% : Binding Energy (ev) Variable 3 Name 1s 1s 1s Pos FWHM Area At% : Binding Energy (ev) Variable 2 Name 1s Variable 4 Pos FWHM Area At% : Binding Energy (ev) Name 1s FWHM Area At% : Binding Energy (ev) XPS Analysis of treated PS nano-spheres Instrument: Axis-Supra (Kratos Analytical, UK) using monochromatic Al Kα radiation (225 W) (thanks to the Dept. Chemistry, UoL) Survey scan pass energy of 160 ev (1 ev step). Narrow region scans pass energy of 20 ev (0.1 ev step size) Plasma processing runs: Oxygen, Acrylic acid, Allylamine monomers: all 120 s deposition time, 20 W (CW RF) power, 60 mtorr (8 Pa) pressure x 10 4 x 10 3 x 10 2 CPS CPS C No treatment, wide scan, C, O x 10 4 x 10 3 CPS CPS CPS x 10 2 C O2 treatment, wide scan, C, O Variable 4 Variable 2 Name 1s 1s 1s Pos FWHM Area At% : Binding Energy (ev) Variable 5 Name 1s FWHM Area At% : Binding Energy (ev) : N 1s Binding Energy (ev) x 10 4 x 10 3 x 10 2 x 10 1 Name 1s 1s Pos FWHM Area At% Binding Energy (ev) CPS Variable 3 Name 1s FWHM Pos FWHM Area Area At% 3.257e At% 3.257e Binding Energy (ev) C1s 285 ev, O1s 531 ev N1s 400 ev CPS N 1s CPS CPS C CPS Allylamine, wide scan, C, O, N x 10 4 x 10 3 Si 2p x 10 3 CPS CPS C Acrylic acid wide scan, C, O

20 XPS Results C O N S Si Polystyrene (PS) O 2 plasma PS Allylamine PS Acrylic acid PS General elements detected from wide scan C1 scan C-C/C-H C-O C=O/O-C-O/C=N/C- OR O=C-O π-π* Polystyrene (PS) O 2 plasma PS Allylamine PS Acrylic acid PS * No functional retention ( COOH NH 2 ) data yet it will require chemical derivatization

21 Plasma Functionalization of Graphene Graphene is a flat, atomic-scale, honeycomb lattice of carbon atoms with a hexagonal atomic structure. The world s first 2D material which extends only in length and width. Graphene can dramatically improve the thermal and electrical conductivity of the medium it is added to, and significantly increases strength. However, graphene is inherently inert and it does not always bond properly with the matrix on its own. Challenges Zero band gap Agglomerates Difficulty in dispersing in liquids

22 Graphene nanoplatelets (approx. 200 nm black powder) Plasma treatment: Oxygen Acrylic acid Allylamine Video of graphene powder shaking W power, 50 mtorr pressure, s deposition time Chemical Analysis: Raman Spectroscopy XPS FTIR Dispersion in liquids Video of graphene powder shaking -2

23 Raman spectroscopy Oxygen plasma treatment Vendor Vendor 2 Intensity mins D G 2 mins 2D 0 mins mins 2 mins graphene Wavenumber (cm -1 ) D/G ratio and 2D/G suggests non pristine - Be careful what you purchase! No extra damage from plasma 20 ev ions

24 FTIR analysis of oxygen plasma treated graphene 0.45 Wavelength Bond Alkyl C-H stretch 1700 C=O bs C-C stretch in ring C-C stretch, C-H bend C-O bond stretch 953, 960 C-H bonds Wavenumber [cm-1] Overlaid FTIR spectra of untreated graphene (green), graphene treated with O 2 plasma 90 sec, 20 W (blue) and O 2 plasma for 180 sec, 50 W (red)

25 XPS Analysis oxygen plasma treated graphene Parameter Total acq. time 24 mins 1.2 secs No. Scans 1 Lens Mode Analyser Mode Energy Step Size ARXPS CAE : Pass Energy 50.0 ev ev No. of Energy Steps 1201 Elemental ID and Quantification Name Peak BE FWHM ev Area (P) CPS.eV Atomic % Q C1s O1s Name Peak BE FWHM ev Area (P) CPS.eV Atomic % Q C1s O1s No treatment O 2 plasma for 90 sec, 20 W Name Peak BE FWHM ev Area (P) CPS.eV Atomic % Q C1s O1s O 2 plasma for 180 sec, 50 W

26 Dispersion in distilled water 10 seconds after shaking Untreated and sonicated Acrylic acid, sonicated Acrylic acid different process! Acrylic acid non sonicated different process! Acrylic acid different process! 2 hours after shaking

27 CNT Growth: Plasma arc in liquids Carbon electrodes, Post-synthesis RF plasma treatment of MWCNT and SWCNT s N 2 Plasma LN 2 or H 2 O, DC,35 Amps up to 38V Production rate 1.0 mg/min Novel characteristics of N 2 functionalised CNTs for molecular devices Source Samples on grounded electrode 10 Watts 10 mtorr 10 mins treatment Drain A N Sano et al, J. App. Phys. 92, 5, 2783, 2002 B Gate Au SiO2 Si Al

28 Conclusions A vacuum plasma-based techniques to functionalize a host of nano and microparticulate materials has been developed. Surface analysis shows efficient surface modification for a range of potential applications. Preliminary studies will be extended to determine better the degree of functional retention and controlled deposition.

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