Nonvolatile, Multicolored Photothermal Writing of Block Copolymer Structural Color

In spite of efforts to fabricate stimuli-sensitive structural colors (SCs) of self-assembled block copolymer (BCP) photonic crystals (PCs) with potential applications in displays, media boards, and sensors, few studies have demonstrated BCP PCs suitable for high-density nonvolatile information storage. Herein, a simple but robust route for multilevel nonvolatile information recording using a BCP PC is presented. The proposed method is based on the spatially controlled crosslinking of microdomains of a BCP PC induced by photothermal conversion. Photothermal SC writing is accomplished via time- and position-controlled laser exposure on thin poly(styrene-block-quaternized 2-vinyl pyridine) (PS-b-QP2VP) PC films deposited on a layer of poly(3,4-ethylenedioxythiophene) doped with tosylate (PP-PEDOT). Upon near-infrared (NIR) irradiation of this structure, the PP-PEDOT underlayer converts the NIR light into thermal energy in the locally irradiated region, which is subsequently transferred to the BCP top layer consisting of alternating in-plane PS and QP2VP lamellar stacks. The QP2VP layers are vulnerable to thermal crosslinking, giving rise to locally programmable SCs. The degree of crosslinking of the QP2VP domains depends on the laser power and exposure time, which allows for multi-SC recording per spot, leading to a novel multilevel optical recording medium based on BCP PCs.