Hydrophobic End‐Modulated Amino‐Acid‐Based Neutral Hydrogelators: Structure‐Specific Inclusion of Carbon Nanomaterials

Abstract

Hydrophobic end‐modulated l‐phenylalanine‐containing triethylene glycol monomethyl ether tagged neutral hydrogelators (1–4) are developed. Investigations determine the gelators’ structure‐dependent inclusion of carbon nanomaterials (CNMs) in the self‐assembled fibrillar network (SAFIN). The gelators (1, 3, and 4) can immobilize water and aqueous buffer (pH 3–7) with a minimum gelator concentration of 10–15 mg mL−1. The hydrophobic parts of the gelators are varied from a long chain (C‐16) to an extended aromatic pyrenyl moiety, and their abilities to integrate 1 D and 2 D allotropes of carbon (i.e., single‐walled carbon nanotubes (SWNTs) and graphene oxide (GO), respectively) within the gel are investigated. Gelator 1, containing a long alkyl chain (C‐16), can include SWNTs, whereas the pyrene‐containing 4 can include both SWNTs and GO. Gelator 3 fails to incorporate SWNTs or GO owing to its slow rate of gelation and possibly a mismatch between the aggregated structure and CNMs. The involvement of various forces in self‐aggregated gelation and physicochemical changes occurring through CNM inclusion are examined by spectroscopic and microscopic techniques. The distinctive pattern of self‐assembly of gelators 1 and 4 through J‐ and H‐type aggregation might facilitate the structure‐specific CNM inclusion. Inclusion of SWNTs/GO within the hydrogel matrix results in a reinforcement in mechanical stiffness of the composites compared with that of the native hydrogels.Neutral hydrogelators with hydrophobicity variation upon going from a C‐16 alkyl chain to an extended aromatic moiety, pyrene, are developed. The C‐16‐containing gelator can include a 1 D allotrope of carbon (SWNT=single‐walled carbon nanotubes), and the pyrene‐containing gelator, with its additional π–π stacking interactions, can incorporate both 1 D and 2 D (GO=graphene oxide) allotropes (see figure).