Gyroid Nickel Nanostructures from Diblock Copolymer Supramolecules

Summary

This article describes the preparation of well-ordered nickel nanofoams via electroless metal deposition onto nanoporous templates obtained from self-assembled diblock copolymer based supramolecules.

Abstract

Nanoporous metal foams possess a unique combination of properties - they are catalytically active, thermally and electrically conductive, and furthermore, have high porosity, high surface-to-volume and strength-to-weight ratio. Unfortunately, common approaches for preparation of metallic nanostructures render materials with highly disordered architecture, which might have an adverse effect on their mechanical properties. Block copolymers have the ability to self-assemble into ordered nanostructures and can be applied as templates for the preparation of well-ordered metal nanofoams. Here we describe the application of a block copolymer-based supramolecular complex - polystyrene-block-poly(4-vinylpyridine)(pentadecylphenol) PS-b-P4VP(PDP) - as a precursor for well-ordered nickel nanofoam. The supramolecular complexes exhibit a phase behavior similar to conventional block copolymers and can self-assemble into the bicontinuous gyroid morphology with two PS networks placed in a P4VP(PDP) matrix. PDP can be dissolved in ethanol leading to the formation of a porous structure that can be backfilled with metal. Using electroless plating technique, nickel can be inserted into the template's channels. Finally, the remaining polymer can be removed via pyrolysis from the polymer/inorganic nanohybrid resulting in nanoporous nickel foam with inverse gyroid morphology.

Introduction

There are several techniques available for the preparation of metal nanofoams: dealloying^1-3, sol-gel approaches^4,5, nanosmelting^6,7, and combustion synthesis⁸. In the dealloying process, the starting material is usually a binary alloy, for example, an alloy of silver and gold. The less noble metal, silver in this case, can be removed either chemically or electrochemically resulting in a disordered porous gold foam with nanosized ligaments. In combustion synthesis, metal is mixed with an energetic precursor that releases energy during its decomposition and drives the formation of metal nanofoam⁸. Studies on the me....

Protocol

1. Preparation and Characterization of PS-b-P4VP(PDP) Complexes with Double Gyroid Morphology

1. Weigh out polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) and pentadecylphenol (PDP, M_r = 304.51 g/mol). In order to obtain the gyroid morphology, carefully select the amount of PDP should be (the weight fraction of P4VP(PDP) block (f_P4VP(PDP))should be ca. 0.6 according to the phase diagram of linear AB diblock copolymers). Usually, 0.15-0.2 g of a PS-b-P4VP leads to PS-b-P4VP(PDP) films 50-100 μm thick (given that the diameter of a Petri dish used in the step 1.3 is 5-6 cm).....

Results

The morphology of supramolecular complexes PS-b-P4VP(PDP)x is examined by TEM and SAXS. Figures 2a and 2b display typical gyroid patterns of a representative supramolecular complex: the double-wave and the wagon-wheel patterns that are known to represent projections through the (211) and the (111) plane of the gyroid unit cell, respectively. The PS block domains appear bright while the P4VP(PDP)x block domains appear dark due to iodine staining. Figure 2c repres.......

Discussion

Supramolecular complexes are successfully applied as precursors for well-ordered metal nanofoams. In this method, the crucial step is to acquire the appropriate template, i.e. a template with gyroid morphology. In the phase diagram of block copolymers the gyroid region is very small and it is rather difficult to target. This means that if conventional block copolymers are used as starting materials, the quite elaborate synthesis has to be repeated until the desired composition, that gives rise to the gyroid.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Reagents
PS-b-P4VP, CAS: 26222-40-2	Polymer Source Inc.	P9009-S4VP P136-S4VP P5462-S4VP P3912-S4VP	additional information are provided in a separate table
PDP	Aldrich	P4402-100G-A	recrystallized twice from petroleum ether
SnCl2	Acros Organics	196981000
PdCl2	Aldrich	76050
NiSO4•H2O	Sigma-Aldrich	227676
Lactic acid	Aldrich	W261106
Citric acid trisodium salt	Sigma-Aldrich	C3674
Borane dimethyl amine complex	Aldrich	180238
PS-b-P4VP catalogue number	Mn (PS), g/mol	Mn(P4VP), g/mol	PDI
P9009-S4VP	24000	9500	1.1
P136-S4VP	31900	13200	1.08
P5462-S4VP	37500	16000	1.3
P3912-S4VP	41500	17500	1.07