Polymer blending as a surface modification technique to alter the wettability of hydrophobic electrospun mats

Abstract

In this thesis, blending as a surface modification technique to change the wettability of hydrophobic electrospun mats was investigated. In the first step, SEBS, chosen as the hydrophobic matrix was blended with amphiphilic PEO-PPO-PEO copolymer. The results showed that hydrophilization was achieved with 15 wt% of PEO-PPO-PEO in the SEBS/PEO-PPO-PEO mats with great surface segregation. But although hydrophilic, this composition presented nonuniform surface coverage and wettability. A microscopic analysis revealed that the composition with 20 wt% of PEO-PPO-PEO presented a peculiar rough interconnected grain-like morphology on the surface of the films and fibers that contributed to more homogeneous surface properties. In the next step, three different types of commercially available PEO-PPO-PEO copolymers with different molecular weight and PEO content were used to hydrophilize SEBS. Segregation to the surface increased in the blends of SEBS with smaller PEO-PPO-PEO molecules with higher proportion of hydrophobic PPO blocks. Hydrophilization was achieved with as little as 5 wt% of PEOPPO-PEO and complete surface saturation was also observed at higher PEO-PPO-PEO contents. Blends with liquid PEO-PPO-PEO presented leaching when in contact with water. High-speed imaging and wicking measurements were performed to distinguish between different hydrophilic mats, and the results showed that the spreading time and wicking rate varied greatly according to the level of segregation and the type of PEO-PPO-PEO used in the blends. The last part of this thesis is a comparison of blending hydrophobic polymers with either hydrophilic PEO or amphiphilic PEO-PPO-PEO polymers to achieve hydrophilization. The results showed that the presence of low surface energy PPO blocks greatly increased the segregation of PEO-PPO-PEO. Blends with pure PEO presented surface depletion and hydrophilization was not achieved in the range of compositions tested (0-20 wt%). Surprisingly, the segregation of PEO-PPO-PEO continued over weeks at room temperature. Theoretical results showed that the equilibrium morphology for the SEBS/PPO system corresponds to a complete wetting layer of PPO over SEBS, which supports the experimental results of complete coverage for some of the SEBS/PEO-PPO-PEO blends and also the aging results that showed a continued segregation to form a PPO layer. The ability of the matrix to allow PEO-PPO-PEO movement over time was also analyzed by comparing the segregation of this copolymer inside SEBS and pure PS. The former presented major segregation due to a higher fraction of free volume at room temperature while the latter practically presented no segregation over time.

Date	19 Dec 2016
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Nicole R. Demarquette (Supervisor)