Fabricating Reactive Surfaces with Brush-like and Crosslinked Films of Azlactone-Functionalized Block Co-Polymers

Summary

Surface fabrication methods for patterned deposition of nanometer thick brushes or micron thick, crosslinked films of an azlactone block co-polymer are reported. Critical experimental steps, representative results, and limitations of each method are discussed. These methods are useful for creating functional interfaces with tailored physical features and tunable surface reactivity.

Abstract

In this paper, fabrication methods that generate novel surfaces using the azlactone-based block co-polymer, poly (glycidyl methacrylate)-block-poly (vinyl dimethyl azlactone) (PGMA-b-PVDMA), are presented. Due to the high reactivity of azlactone groups towards amine, thiol, and hydroxyl groups, PGMA-b-PVDMA surfaces can be modified with secondary molecules to create chemically or biologically functionalized interfaces for a variety of applications. Previous reports of patterned PGMA-b-PVDMA interfaces have used traditional top-down patterning techniques that generate non-uniform films and poorly controlled background chemistries. Here, we describe customized patterning techniques that enable precise deposition of highly uniform PGMA-b-PVDMA films in backgrounds that are chemically inert or that have biomolecule-repellent properties. Importantly, these methods are designed to deposit PGMA-b-PVDMA films in a manner that completely preserves azlactone functionality through each processing step. Patterned films show well-controlled thicknesses that correspond to polymer brushes (~90 nm) or to highly crosslinked structures (~1-10 μm). Brush patterns are generated using either the parylene lift-off or interface directed assembly methods described and are useful for precise modulation of overall chemical surface reactivity by adjusting either the PGMA-b-PVDMA pattern density or the length of the VDMA block. In contrast, the thick, crosslinked PGMA-b-PVDMA patterns are obtained using a customized micro-contact printing technique and offer the benefit of higher loading or capture of secondary material due to higher surface area to volume ratios. Detailed experimental steps, critical film characterizations, and trouble-shooting guides for each fabrication method are discussed.

Introduction

Developing fabrication techniques that allow for versatile and precise control of chemical and biological surface functionality is desirable for a variety of applications, from capture of environmental contaminants to development of next generation biosensors, implants, and tissue engineering devices^1,2. Functional polymers are excellent materials for tuning surface properties through "grafting from" or "grafting to" techniques³. These approaches allow for control of surface reactivity based on the chemical functionality of the monomer and molecular weight of the polymer....

Protocol

1. PGMA-b-PVDMA Synthesis²⁰

1. Synthesis of PGMA macro-chain transfer agent (Macro-CTA)
   1. Use a 250-mL round-bottom reaction flask equipped with a polytetrafluoroethylene-coated magnetic stir bar.
   2. Combine 14.2 g of glycidyl methacrylate GMA (142.18 g/mol) with 490.8 mg of 2-cyano-2-propyl dodecyl trithiocarbonate (CPDT) (346.63 g/mol), and 87.7 mg of 2,2′-azobis (4-methoxy-2,4-dimethyl valeronitrile) (V-70) (308.43 g/mol) (molar ratio of CPDT: V-70 = 5:1), and benzene (100 mL) into air free round bottom flask.
   3. Degas the reaction mixture using argon and stir for 30 min. Subsequently put the soluti....

Results

Contact angle measurements can be used to evaluate the functionalization of silicon with PGMA-b-PVDMA. Figure 1 depicts the contact angle of the silicon substrate during the different processing steps. Hydrophilic behavior of the plasma cleaned silicon substrate is shown in Figure 1B. The contact angle after polymer spin coating and annealing is 75° ± 1°(Figure 1C) which is consi.......

Discussion

This article presents three approaches to patterning PGMA-b-PVDMA, each with its set of advantages and drawbacks. The parylene lift-off method is a versatile method for patterning block co-polymers at micro to nanoscale resolution, and has been used as a deposition mask in other patterning systems^33,34,35. Due to its relatively weak surface adhesion, the parylene stencil can be easily removed from the surface by sonicat.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Material
Ethanol, ≥ 99.5%	Sigma-Aldrich	459844	-
HCL, 1.019 N in H2O	Fluka Analytical	318949	-
Acetone, ≥ 99.5%	Sigma-Aldrich	320110	-
Benzene, ≥ 99.9%	Sigma-Aldrich	270709	-
Isopropanol, ACS reagent, ≥99.5%	Sigma-Aldrich	190764
Hexane	Fisher Chemical	H292-4	-
Argon	Matheson Gas	G1901175	-
Tetrahydrofuran (THF), ≥ 99.9%	Sigma-Aldrich	401757	-
Pluronic F-127	Sigma-Aldrich	P2443	-
Polydimethyl Siloxane (PDMS) Slygard 184	Dow Corning	4019862	-
Trichloro (1H,1H,2H,2H-perfluorooctyl) silane (TPS), 97%	Sigma-Aldrich	448931	It is toxic. Work with it under hood
Anhydrous Chloroform, ≥ 99%	Sigma-Aldrich	372978	-
Positive Photoresist AZ1512	MicroChemicals	AZ 1512	amber-red liquid, density 1.083 g/cm3, spin coating step should be done under the hood
Developer AZ 300 MIF	MicroChemicals	AZ300 MIF	clear colourless liquid with slight amine odor and density of 1 g/cm3
1,2-Vinyl-4,4- dimethyl azlactone (VDMA)	Isochem North America, LLC	VDMA	-
2-cyano-2-propyl dodecyl trithiocarbonate (CPDT)	Sigma-Aldrich	723037	-
2,2′-Azobis (4methoxy-2,4-dimethyl valeronitrile) (V-70)	Wako Specialty Chemicals	CAS NO. 15545-97-8, EINECS No. 239-593-8	-
Parylene N	Specialty Coating Systems	15B10004	-
Name	Company	Catalog Number	Comments
Equipment
Parylene Coater	Specialty Coating Systems	SCS Labcoater (PDS 2010)	-
Mask alignment system	Neutronix Quintel	NXQ8000	-
Oxygen Plasma Etcher	Oxford Instruments	Plasma Lab System 100	-
Surface Profilometer	Veeco	Dektak 150	Scan type was standard hill. Scan duration and force were 120 s and 1 mg, respectively.
Brightfield Upright Microscope	Olympus Corporation	BX51	-
Oxygen Plasma  Cleaner	Harrick Plasma	PDC-001-HP	-
Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR)	Perkin Elmer	ATR-FTIR 100	-
Atomic Force Microscopy (AFM)	PicoPlus	Picoplus atomic force microscope	Veeco MLCT-E cantilevers with a 0.5 N/m spring constant. Scan speeds varied between 0.25 and 1 Hz.
Scanning Electron Microscopy (SEM)	Hitachi Science Systems Ltd., Tokyo, Japan	-	-
Rotary Tool Workstation	Dremel	Model 220-01	-
Spin Coater	Smart Coater	SC100	-
Vacuum Oven	Yamato Scientific Co.	PCD-C6(5)000)	-
Size Exclusion Chromatography (SEC)	Waters Alliance 2695 Separations Module	720004547EN	-
Refractive Index (RI) detector	Waters	Model 2414	-
Photodiode Array Detector	Waters	Model 2996, 716001286	-
Multi-angle Light Scattering (MALS) Detector	Wyatt Technology	miniDAWN TREOS II	-
Viscometer	Wyatt Technology	Viscostar	-
PLgel 5 µm mixed-C columns (300 x 7.5 mm)	Agilent	5 µm mixed-C columns	-
Ellipsometer	J. A. Woollam	alpha-SE	Cauchy model, PGMA and PVDMA layers had refractive indices of 1.50 and 1.52 at 632 nm
Ultrasonic Sonicator	Fischer Scientific	FS-110H	-