Permeability and Electrokinetic Characterization of Poly(ethylene terephthalate) Capillary Pore Membranes with Grafted Temperature-Responsive Polymers

Abstract

Poly(ethylene terephthalate) (PET) track-etched membranes with average pore diameters of 692 and 1629 nm were functionalized using the monomer N-isopropylacrylamide (NIPAAm) and a photoinitiated "grafting-from" approach in which a surface-selective reaction has been most efficiently achieved by combinations of the unmodified PET surface with benzophenone and, alternatively, of an aminated PET surface with benzophenone carboxylic acid. Consistent estimations of the pore diameters of the base PET membranes and of the effective grafted polyNIPAAm layer thicknesses on the PET pore walls were possible only on the basis of the permeabilities measured with aqueous solutions of higher ionic strength (e.g., 0.1 M NaCl). However, the permeabilities measured with ultrapure water indicated that the "electroviscous effect" was significant for both base membranes. The influences of membrane pore diameter, surface charge, and solution ionic strength could be interpreted in the framework of the space-charge model. Functionalized membranes with collapsed grafted polymer hydrogel layer thicknesses of a few nanometers exhibited almost zero values of the zeta potential estimated from the trans-membrane streaming potential measurements. This was caused by a "hydrodynamic screening" of surface charge by the neutral hydrogel. Very pronounced changes in permeability as a function of temperature were measured for PET membranes with grafted polyNIPAAm layers, and the effective layer thickness in the swollen state--here up to approximately 300 nm--correlated well with the degree of functionalization. The subtle additional effects of solution ionic strength on the hydrodynamic layer thickness at 25 degrees C were different from the effects for the base PET membranes and could be explained by a variation in the degree of swelling, resembling a "salting-out" effect. Overall, it had been demonstrated that the functionalized capillary pore membranes are well suited for a detailed and quantitative evaluation of the relationships between the synthesis, the structure, and the function of grafted stimuli-responsive polymer layers.

Current Rectification in Temperature‐Responsive Single Nanopores

“…[61] For example, Ulbricht et al reported that functionalized membranes covered by a collapsed polymer hydrogel layer of several nanometers thick exhibit almost zero values of zeta potential. [26] The third possible way for the diminishing current rectification is the enlargement of the pore diameter due to the collapse of PNIPAM brushes. [53,62] This assumption can be justified by the parallel experiments conducted on another series of samples with larger tip diameter of~40 nm (see Supporting Information, Figure S4).…”

Protein-selective adsorbers by molecular imprinting via a novel two-step surface grafting method

“…section 3.3.1) [10][11] and a thickness of 23 µm were purchased from Oxyphen GmbH (Dresden, Germany). Regenerated cellulose membranes (RC 60) with 75 m thickness, about 50 mm diameter, and 1.0 m average effective pore diameter were purchased from Whatman, Inc.…”

“…In comparison with the old product which has been used by Ulbricht and his coworkers, [10][11] the distribution of pore size has been extended but is still acceptable. The membrane morphology was further characterized by SEM.…”

Deposition of functionalized calcium phosphate nanoparticles on functionalized polymer surfaces

“…PET track-etched membranes with nominal pore sizes of 400 nm and 1000 nm, respectively, were obtained from Oxyphen (Dresden, Germany); their pore diameters determined by permporometry were 692AE17 nm and 1629AE130 nm, respectively [13]. For oxidative hydrolysis ("carboxylation"), the unmodified PET membranes were immersed in a reaction mixture of 10 g KMnO 4 (Fluka, p.a.)…”