Modified Breath Figure Methods for the Pore-Selective Functionalization of Honeycomb-Patterned Porous Polymer Films

Abstract

Recent developments in the field of the breath figure (BF) method have led to renewed interest from researchers in the pore-selective functionalization of honeycomb-patterned (HCP) films. The pore-selective functionalization of the HCP film gives unique properties to the film which can be used for specific applications such as protein recognition, catalysis, selective cell culturing, and drug delivery. There are several comprehensive reviews available for the pore-selective functionalization by the self-assembly process. However, considerable progress in preparation technologies and incorporation of new materials inside the pore surface for exact applications have emerged, thus warranting a review. In this review, we have focused on the pore-selective functionalization of the HCP films by the modified BF method, in which the self-assembly process is accompanied by an interfacial reaction. We review the importance of pore-selective functionalization, its applications, present limitations, and future perspectives.

Keywords: honeycomb-patterned porous film; interfacial reaction; modified breath figure method; pore-selective functionalization; self-assembly.

Figure 1

A sequence of stages for the preparation of HCP porous film by the breath-figure method. (a) Polymer solution in a volatile solvent under humid conditions; (b) condensation of water droplets due to cooling of surface temperature; (c) water droplets grow bigger and sink into the solution; (d) packing of water droplets; (e) arrangement of water droplets into ordered two- or three-dimensional (2D or 3D) arrays; and (f) formation of HCP film after drying.

Figure 2

Possible site-selective functionalization of HCP films by modified BF method. (a) Top, (b) bottom, and (c) pore surface functionalization.

Figure 3

A sequence of stages of pore-selective functionalization by self-assembly of amphiphilic polymer. (a) Polymer solution containing amphiphilic polymer in a volatile solvent under humid conditions; (b) condensation of water droplets due to cooling of surface temperature; (c) close packing of water droplets and self-assembly of hydrophilic part of the amphiphilic polymer around the water droplets; (d) formation of pore-functionalized HCP film after drying.

Figure 4

(a) Cross-sectional diagram of nanoparticle assembly at a water droplet–solution interface during the breath-figure formation. (b) SEM images of the surface of an NP-decorated BF film. (c) TEM images of cross-sections through porous PS film. Reprinted with permission from ref. [86]. Copyright 2004 Nature Materials.

Figure 5

(a) Synthetic approach to a streptavidin microarray with immobilization of protein selectively in the pores. (b) Confocal microscopy images of PS-PAA honeycomb-structured porous films after modification with biotin and streptavidin. Reprinted with permission from ref. [87]. Copyright 2008 Advanced Materials.

Figure 6

(a) CLSM images of PBA-PAA/PS porous film after their immersion in ARS dye solution. (b) SEM image of porous PS film loaded with insulin aggregates after immersion in 0.8 M NaCl aqueous solution at pH 5.3 at 25 °C. (c) Scheme of the capture of glucose and the glucose-responsive release of insulin aggregates. Reprinted with permission from ref. [95]. Copyright 2015 Journal of Materials Chemistry B.

Figure 7

(a) Schematic representation of the chemical distribution of the blends of PS and PS-b-PPEGMA (75:25 wt% blend) at the surface. Reprinted with permission from ref. [80]. Copyright 2016 ACS Applied Materials & Interfaces. (b) Scheme of the strategy for selective cell culture. Mammalian cells interact only adhere to the top surface, while the bacteria may enter inside the pores due to size differences and get affected by antimicrobial functional groups. (c) Cell adhesion tests using (actin staining (red), and Hoechst (blue)) after 96 h of culture on the fabricated film. Reprinted with permission from ref. [5]. Copyright 2017 ACS Applied Materials & Interfaces.

Figure 8

(a) The schematic representation showing the fabrication of the metal–NPs-functionalized honeycomb films. (b) SEM images of the HCP films filled with metal NPs: Au (A), Ag (B), and Cu (C). Reprinted with permission from ref. [97]. Copyright 2021 Polymers.

Figure 9

(a) Schematic representation of reaction mechanism of Tollens’s reagent with aldehyde group in HCP porous films fabricated using PS and PS-CHO blended solutions. (b) The typical SEM images of PS/PS-CHO HCP porous films with Ag functionalization after treating with Tollens’s reagent. Reprinted with permission from ref. [98]. Copyright 2018 Polymer Physics.

Figure 10

(a) Proposed formation mechanism of hybrid membranes with AuNPs inside the pores of the HCP film. (b) SEM analysis of sample Au5 after heating at 170 °C for 5 min, showing AuNPs present at the pores. Reprinted with permission from ref. [70]. Copyright 2021 Colloids and Surfaces A: Physicochemical and Engineering Aspects.

Figure 11

A sequence of stages of pore-selective functionalization by self-assembly accompanied by chemical reaction. (a) polymer solution containing reactant A, (b) condensation of water droplets containing counter reactant B, (c) functionalizing of product C at the pore by the interfacial reaction of reactant A and reactant B, (d) formation of pore-functionalized HCP film after drying.

Figure 12

Pore-selective functionalization of HCP films by using water as a reactant. The polymer solution containing a reactant reactive to water is cast under humid conditions for the reaction to occur at the interface of polymer solution/water droplet to achieve pore-selective functionalization.

Figure 13

(a) Scheme for the formation of highly ordered asymmetrical inorganic particle/polymer composite films by BFs method. (b,c) SEM images of the obtained composite film from the TiCl₄/PS/CHCl₃ solution with different concentrations of TiCl₄, SEM images of (c) hemispherical and (d,e) mushroom-like TiO₂ microparticles after calcination of the composite film at 450 °C for 3 h. Reprinted with permission from ref. [102]. Copyright 2011 Journal of the American Chemical Society.

Figure 14

(a) Schematic representation showing different reaction conditions with the variance in time intervals of pouring (Ti(C₄H₉O)₄) solution to the PS solution. (b–e) shows the typical SEM images of PS film obtained at a different time interval. Reprinted with permission from ref. [104]. Copyright 2018 Polymer.

Figure 15

SEM images of porous PACA films fabricated from monomer solutions of (a) ECA, (c) BCA, (e) OCA, and polymer solutions of (b) PECA, (d) PBCA, (f) POCA. Reprinted with permission from ref. [106]. Copyright 2010 Journal of Colloid and Interface Science.

Figure 16

(a) Mechanism showing the formation of PANI-f-PS film with PANI functionalized pores: (i) Condensed aq. aniline hydrochloride droplets on PS-BPO solution during BF process, (ii) assembly of aniline hydrochloride and BPO at aqueous droplet/polymer solution interface, (iii) interfacial polymerization, (iv) and formation of PANI functionalized pores after completion of reactive BF process. (b) SEM, (c) optical, and (d) digital photograph of PANI-f-PS film. Reprinted with permission from ref. [110]. Copyright 2017 Polymer.

Figure 17

(a) Schematic representation showing the fabrication of the pore-selective carboxyl functionalized PI HCP films (PI-COOK) via BF method under aq. KOH humidity with a time interval after using initial water humidity. SEM images of PI films fabricated under (b) water humidity, (c) aq. KOH humidity, and (d) under aq. KOH humidity for 20 min after initial water humidity. Reprinted with permission from ref. [111]. Copyright 2018 Polymer.

Figure 18

(a) Schematic representation showing the experimental process for the pore-selective SnS-functionalized PS HCP film using a modified BF method. SEM images of PS HCP films fabricated by casting PS solution containing SnCl₂ under (b,c) aq. H₂S humidity, and (d) magnified TEM image showing a thin layer of SnS. Reprinted with permission from ref. [109]. Copyright 2018 Advanced Materials Interfaces.

Figure 19

(a) The possible mechanism involved in the rBF process via self-assembly process accompanying an interfacial chemical reaction between formylated PS and oxone at the interface of the water droplet/polymer solution. (b) Schematic process for the preparation of pore-selective PNIPAAm modified (PS-pf-PNIPAAm) film by the reaction between PS-pf-COOH film and an aq. H₂N-PNIPAAm solution in the presence of EDC. (c,d) SEM images and elemental mapping show the capture of Ag particles at 25 °C and 40 °C. Reprinted with permission from ref. [112] Copyright 2020 Polymer. (e) Scheme showing the release of rhodamine B at the LCST of PNIPAAm. Reprinted with permission from ref. [115] Copyright 2021 Polymer Bulletin.

Figure 20

(a) Schematic representation showing the fabrication of the pore-selective Ag functionalized PS HCP films via rBF method under aq. AgNO₃ humidity. Typical SEM images of the 10 and 20 wt% PS HCP films fabricated under (b,d) aq. humidity, and (c,e) aq. AgNO₃ humidity, respectively. (f) The mechanism for trapping of bacteria inside the pits of the Ag-functionalized porous HCP film. SEM images of (g) E. coli and (h) S. aureus showing the trapped bacteria at the pores of the HCP film. Reprinted with permission from ref. [119] Copyright 2022 Polymer.

Figure 21

Pore-selectively functionalized HCP films via the modified BF method and their applications in biology, medical, sensor application, and catalysis. PSFF—Pore-Selectively Functionalized Film.