Defining Swelling Kinetics in Block Copolymer Thin Films: The Critical Role of Temperature and Vapour Pressure Ramp

Polymers

Cian Cummins¹  Timothy W. Collins²  Sudhakara Naidu Neppalli³  Parvaneh Mokarian-Tabari³  Zahra Gholamvand³  Michael A. Morris³ 

[1] Centre de Recherche Paul Pascal (CRPP), The French National Centre for Scientific Research (CNRS), University of Bordeaux, UMR 5031, 115 Avenue Schweitzer, 33600 Pessac, France;Department of Chemistry, University College Cork, Tyndall National Institute, T12 K8AF Cork, Ireland;School of Chemistry, The University of Dublin, Trinity College Dublin, D02 PN40 Dublin, Ireland;

关键词: block copolymer;    phase separation;    solvent vapour annealing;    ramp rate;    kinetic mechanism;   

DOI  :  10.3390/polym13234238

来源: DOAJ

【 摘 要 】

We studied the kinetics of swelling in high-χ lamellar-forming poly(styrene)-block- poly(lactic acid) (PS-b-PLA) block copolymer (BCP) by varying the heating rate and monitoring the solvent vapour pressure and the substrate temperature in situ during solvo-thermal vapour annealing (STVA) in an oven, and analysing the resulting morphology. Our results demonstrate that there is not only a solvent vapour pressure threshold (120 kPa), but also that the rate of reaching this pressure threshold has a significant effect on the microphase separation and the resulting morphologies. To study the heating rate effect, identical films were annealed in a tetrahydrofuran (THF) vapour environment under three different ramp regimes, low $(r_T<1 °\mathrm{C}/\min$), medium $\left(2<r_T<3 °\mathrm{C}/\min \right)$ and high $(r_T>4 °\mathrm{C}/\min )$, for 60, 90 and 120 min, respectively, while the solvent vapour pressure and the substrate temperature were measured in real time. The translational order improved significantly with increasing the heating rate. The solvent mass uptake calculated for the different ramp regimes during annealing is linearly proportional to time, indicating that the swelling kinetics followed Case II diffusion. Two stages of the swelling behaviour were observed: (i) diffusion at the initial stages of swelling and (ii) stress relaxation, controlled at later stages. Films with a faster rate of increase in vapour pressure $(r_P>2 \mathrm{kPa}/\min$) reached the pressure threshold value at an early stage of the swelling and attained a good phase separation. According to our results, highly ordered patterns are only obtained when the volume fraction of the solvent exceeds the polymer volume fraction, i.e., $({\phi }_s\ge {\phi }_p)$_, during the swelling process, and below this threshold value $({\phi }_s=0.5)$, the films did not obtain a good structural order, even at longer annealing times.

【 授权许可】

Unknown