Visualizing Penetration of Fluorescent Dye through Polymer Coatings

Abstract

Understanding how small molecules penetrate and contaminate polymer films is of vital importance for developing protective coatings for a wide range of applications. To this end, we visualize how rhodamine B fluorescent dye diffuses through polystyrene‐polydimethylsiloxane block copolymer coatings using confocal microscopy. The intensity of dye inside the coatings grows and decays non‐monotonically, which is likely due to a combination of dye molecule transport occurring concurrently in different directions. An empirical fitting equation allows us to compare the contamination rates between copolymers, demonstrating that dye penetration is related to the chemical makeup and configuration of the block copolymers. Our work shows that confocal microscopy can be a useful tool to visualize the transport of a fluorophore in space and time through a coating.This article is protected by copyright. All rights reserved

Controlling Anti-Penetration Performance by Post-Grafting of Fluorinated Alkyl Chains onto Polystyrene-block-poly(vinyl methyl siloxane)

“…In our recent publication, for all PS-b-PDMS species, a nonmonotonic behavior was seen�there was a short, rapid increase, followed by a peak formation at time t = t peak , and then a slower decrease to a steady-state value. 42 We hypothesized that a similar nonmonotonic behavior in the penetration of PS-b-PVMS block copolymers seen here occurred through two concurrent directional penetration processes termed P1 and P2 (Figure 4a), which are governed by the thin geometry of the coating and not by an inherent material property (noting that we are only visualizing a small region in our imaging window, represented as a yellow box in Figure 4a). The faster process P1, which occurs along the micrometer-scale thickness of the coating in the vertical direction, is responsible for the rapid influx and accumulation of the dye, causing an increase in fluorescence intensity.…”

“…A more detailed setup and description of the penetration experiment can be found in the Experimental Section and in our previous publication. 42 The fluorescence intensity distribution in the coating is shown for the polymers with different fluorinations (Figure 4d−i).To obtain a more intuitive understanding of the change in penetration kinetics, the intensity inside the coating is integrated along the spatial vertical axis to obtain the total change in fluorescence inside the coating over time (Figure 4b). This value is normalized by the thickness (∼10 μm) of the respective coating because there is a minor variation in thickness across samples, and this normalized intensity is written with the units of [intensity]/ [length] or px/μm.…”

“…This value is normalized by the thickness (∼10 μm) of the respective coating because there is a minor variation in thickness across samples, and this normalized intensity is written with the units of [intensity]/[length] or px /μm. In our recent publication, for all PS- b -PDMS species, a nonmonotonic behavior was seenthere was a short, rapid increase, followed by a peak formation at time t = t peak , and then a slower decrease to a steady-state value . We hypothesized that a similar nonmonotonic behavior in the penetration of PS- b -PVMS block copolymers seen here occurred through two concurrent directional penetration processes termed P1 and P2 (Figure a), which are governed by the thin geometry of the coating and not by an inherent material property (noting that we are only visualizing a small region in our imaging window, represented as a yellow box in Figure a).…”

“…Details of the penetration tests and image analysis are described in a recent publication. 42 Briefly, the substrates used for the coatings were glass coverslips of thickness ∼0.15 mm that were cleaned using soap solution, distilled water, and ethanol, dried, and then placed in a UV−Ozone chamber for surface treatment. PS-b-P(n-C x F 2x+1 -VMS) was thoroughly dissolved in THF (30% by weight) and spin-coated onto the treated glass coverslips such that the film thickness was approximately 10 μm.…”

“…41 And our recent antipenetration paper on block copolymers of PS-b-PDMS indicated that a higher weight fraction of PDMS would reduce surface coatings' anti-penetration properties. 42 In this paper, we present an easy and effective method to directly functionalize PDMS with a series of fluorinated alkyl chains by thiol−ene click reactions 41 to gradually tune its material properties and study anti-penetration behavior. The addition of fluorinated alkyl chains to PDMS is expected to improve its anti-penetration properties because of the hydrophobicity and oleophobicity of fluorinated alkyl chains, which can suppress wetting by solvents and subsequent penetration.…”