Controlled Bulk Properties of Composite Polymeric Solutions for Extensive Structural Order of Honeycomb Polysulfone Membranes

Abstract

This work provides additional insights into the identification of operating conditions necessary to overcome a current limitation to the scale-up of the breath figure method, which is regarded as an outstanding manufacturing approach for structurally ordered porous films. The major restriction concerns, indeed, uncontrolled touching droplets at the boundary. Herein, the bulk of polymeric solutions are properly managed to generate honeycomb membranes with a long-range structurally ordered texture. Water uptake and dynamics are explored as chemical environments are changed with the intent to modify the hydrophilic/hydrophobic balance and local water floatation. In this context, a model surfactant such as the polyoxyethylene sorbitan monolaurate is used in combination with alcohols at different chain length extents and a traditional polymer such as the polyethersufone. Changes in the interfacial tension and kinematic viscosity taking place in the bulk of composite solutions are explored and examined in relation to competitive droplet nucleation and growth rate. As a result, extensive structurally ordered honeycomb textures are obtained with the rising content of the surfactant while a broad range of well-sized pores is targeted as a function of the hydrophilic-hydrophobic balance and viscosity of the composite polymeric mixture. The experimental findings confirm the consistency of the approach and are expected to give propulsion to the commercially production of breath figures films shortly.

Keywords: breath figure membranes; extensively ordered textures; water self-assembly.

Figure 1

Representative scheme of formation of ordered porous membranes according to breath figure method.

Figure 2

SEM micrographs related to a honeycomb membrane prepared from a PSU/DCM/2-propanol solution: (a) top surface and (b) cross-section of the membrane.

Figure 3

Effects of the surfactant loading on the kinematic viscosity of the PSU/DCM/2-propanol (12 wt %) solutions.

Figure 4

Changes in the pore size and distribution with rising content of surfactant (a); Effects of surfactant/alcohol complex on membrane morphology (SEM micrographics (b–d) and formation of aggregates in precursor polymeric solutions (Dynamic Light Scattering (a’–d’)).

Figure 5

Estimation of interfacial tension values between a water droplet and polymeric solution containing increasing amount of surfactant.

Figure 6

Variation of pore size (a) and pore distribution (b) as a function of the different length and bulky chain of alcohols contained in PSU/DMC solutions with surfactant at 10⁻⁴ M.

Figure 7

Geometric pore size vs. kinematic viscosity for solutions (o) containing surfactant at 10⁻⁴ M and alcohols with different length and bulky chains.