Nanoobjects coming from mesomorphic ionic PAMAM dendrimers

Abstract

A series of ionic amphiphilic dendrimers constituted by the grafting of poly(amidoamine) (PAMAM) of different generations (G = 0–4) with linear carboxylic acids bearing hydrophobic chains has been prepared. Their self-assembly tendency both in bulk and in water has been investigated. Almost all of the compounds present liquid crystalline behaviour as shown by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X-ray diffractometry (XRD) studies. Smectic A mesomorphism has been found for all of the compounds and rectangular columnar mesophase is displayed for the highest generation compound at low temperature. Interestingly these amphiphilic dendrimers are also capable to self-assemble in water depending on their hydrophobic/hydrophilic balance forming some nanoobjects. In most of the cases these nanoobjects resemble nanospheres whose morphology has been studied by means of transmission electronic microscopy (TEM). The stability of these nanospheres is disrupted in acid or basic media and their amphiphilic nature makes it possible for them to host both hydrophobic (β-carotene) and hydrophilic (Rhodamine B) molecules.