Thin films of cellulose derivatives

Transcription

1 LIGNCELLVALUE-ADDED MATERIALS AND FUNCTINAL STRUCTURES FRM LIGNCELLULSICS Thin films of cellulose derivatives Steering group meeting Laura Taajamaa UTLINE Background - Thin films - Polymer blends - Cellulose derivatives - Spin coating - bjective Experimental Hypothesis for morphology formation Conclusions 1

2 Background - THIN FILMS MTIVATIN FR THIN FILMS Modeling aspect - well-defined chemistry - well-defined morphology Materials aspect - sensors - transistors - photonic devices - receptors - templated nanomaterials - coatings etc. Background - PLYMER BLENDS Polymer blend: two or more macromolecular substances blended to create a new material with novel physical properties Immiscible polymer blends phase separate during spin coating. The patterns formed are regular due to the constraints caused by the interfaces. Solvent Start nephase region End Two-phase region Component 1 Component 2 Figure adopted from: Gutmann et al., Faraday Discuss., 1999, 112,

3 * H H DMAc/LiCl, HMDS n * Background CELLULSE DERIVATIVES Trimethylsilyl HCl/water cellulose (g) (TMSC) DS=3 * (CH 3 ) 3 Si Si(CH 3 ) 3 n * Si(CH 3 ) 3 Gas phase acid conversion Cellulose triacetate (CTA) DS=3 Ac Ac n Ac = Ac - Gas phase basic conversion Cellulose Cellulose After either of the blend components has been converted to cellulose, the remaining one can be selectively dissolved Alternatively, also the second component can be converted to cellulose Background - SPIN CATING A method to cast films from dissolved or dispersed substance by removing the solvent with high speed spinning Liquid film, becoming solid Fluid flow Evaporation Substrate Fluid flow w Spinning speed in general: rpm 3

4 Background BJECTIVE A matrix of materials with unique morphological and surface energy properties TMSC/CTA Cellulose/CTA TMSC/Cellulose Cellulose/- Cellulose/Cellulose -/Cellulose Cellulose/Cellulose EXPERIMENTAL APPRACH Ultrathin ( 100 nm) cellulose derivative films TMSC/CTA blend solutions in chloroform TMSC/CTA films on hydrophilic silica Cellulose/CTA films Cellulose/- films Spin coating 4000 rpm Conversion of TMSC to cellulose Selective dissolution of CTA with chloroform AFM (atomic force microscopy) XPS (X-ray photoelectron spectroscopy) CA (Contact angle measurements) 4

5 ULTRATHIN CELLULSE DERIVATIVE FILMS AFM TMSC conversion TMSC/CTA films Cellulose/CTA films CTA dissolution Cellulose/- films Lateral phase separation ULTRATHIN CELLULSE DERIVATIVE FILMS AFM TMSC conversion TMSC/CTA films Cellulose/CTA films CTA dissolution Cellulose/- films High rims around the pores 5

6 ULTRATHIN CELLULSE DERIVATIVE FILMS AFM M o r e C T A Humidity and blend ratio played an important role in the morphology formation Pore growth essentially linked to CTA rich phase, but presence of humid air vital Humidity increases ULTRATHIN CELLULSE DERIVATIVE FILMS AFM TMSC conversion TMSC/CTA films Cellulose/CTA films CTA dissolution Cellulose/- films Pores concentrated on areas rich in CTA TMSC layer on top of the solid support 6

7 Relative C emission / % Relative amount of silicon / % ULTRATHIN CELLULSE DERIVATIVE FILMS AFM The pore density increased as CTA fraction increased ULTRATHIN CELLULSE DERIVATIVE FILMS XPS C emission - fingerprint for CTA Silicone amount - fingerprint for TMSC CTA fraction CTA fraction Both vertical and horizontal phase separation 7

8 Contact angle / degrees ULTRATHIN CELLULSE DERIVATIVE FILMS CA 1: TMSC/CTA blend ratio 1:1 0: TMSC/CTA films Cellulose/- films Thin layer of TMSC prevailed also on the air-film interface in all blend ratios 50 Cellulose/CTA films CTA fraction The effect of roughness in the same order of magnitude with standard deviation MAIN EXPERIMENTAL BSERVATINS Both vertical and horizontal phase separation AFM, XPS TMSC formed a layer next to the substrate AFM Thin layer of TMSC also on the air-film interface CA Humidity and blend ratio played an important role in the morphology formation AFM Pore growth linked essentially to CTA rich phase, but presence of humid air also vital AFM By increasing the fraction of CTA in the original spin coating solution, the surface density of pores increased AFM 8

9 HYPTHESIS MRPHLGY FRMATIN Transient bilayer theory (blend ratios with excess of one component): Entropic optimization vertical phase separation upper CTA layer dewets holes filled by the TMSC-rich layer from underneath (lateral phase separation) Intermediate blend ratios: breath figures or additional dewetting Layer inversion: Film strives to minimize its surface energy material from the lower layer forms a continuous layer at the topmost surface FAVRED Dewetting Breath figures CNCLUSINS A versatile matrix of ultrathin bicomponent cellulose derivative films with phase-specific pore formation was presented Reasons behind genesis and evolution of morphology were scrutinized Morphology formation various consecutive phenomena - vertical and lateral phase separation - dewetting under humid atmosphere - layer inversion 9

10 CMMUNICATIN CNFERENCES: - Non-woven fiber mats from cellulose derivative blends: American Chemical Society Spring 2011 National Meeting & Exposition, March 27-31, Anaheim, CA - Travel grant from Emil Aaltonen Foundation: International Symposium on Surface Science, Towards Nano-,Bio-, and Green Innovation (December 2011, Japan) SEMINAR PRESENTATIN: - Phase-specific pore growth in cellulose-based polysaccharide films: The Graduate school for biomass refining BIREGS Summer seminar (June 7-8, Naantali) MANUSCRIPTS: - Phase-specific pore growth in ultrathin bicomponent films from cellulosebased polysaccharides: submitted to ACS Nano - Electrospun cellulose derivative blends: in preparation ACKNWLEDGEMENTS Janne, Eero Kontturi & rlando Leena-Sisko Johansson & Joe Campbell XPS measurements 10

11 LIGNCELLVALUE-ADDED MATERIALS AND FUNCTINAL STRUCTURES FRM LIGNCELLULSICS Thank you! Questions, comments? 11