Nanoparticles and Polymers. Bricks and Mortar Self-Assembly of Nanostructures
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Nanoparticles and Polymers. Bricks and Mortar Self-Assembly of Nanostructures Andrew Boal, Faysal Ilhan, Vincent Rotello,* Thomas Russell1 Dept. of Chemistry,1Dept. of Polymer Science and Engineering, University of Massachusetts, Amherst, MA 01003 USA ABSTRACT Polymers provide a useful tool for the controlled assembly of colloidal nanoparticles. We have developed a bricks and mortar strategy in which colloidal gold particles functionalized with recognition elements serve as the bricks and polymers bearing complementary functionality serve as mortar to hold together the nanoparticles. In this methodology, the conformational flexibility of the polymer compensates for irregularities in the size and shape of the aggregate structure. We have used this method to create discrete micrometer-scale spherical assemblies based on 2 nm gold nanoparticles. Both the size and shape of these assemblies can be controlled, providing spherical assemblies ranging from 50 nm to 1500 nm, as well as network structures. DISCUSSION To provide a general means for the controlled self-assembly of nanoparticles, we have developed a bricks and mortar approach. In this strategy, colloidal gold particles functionalized with recognition elements serve as the bricks, while polymers bearing complementary functionality serve as mortar, holding together the colloidal particles. Using this strategy, the conformational flexibility of the polymer compensates for irregularities in the size and shape of the aggregate structure, allowing the efficient propagation of order during the self-assembly process.1 Complementarity between colloid and polymer was achieved using diaminotriazine-thymine three-point hydrogen bonding interaction (Figure 1a). For the polymer component, diaminotriazine-functionalized polystyrene 1 was employed (Figure 1b).2 The required thyminefunctionalized colloids were synthesized starting with ~2 nm gold particles covered with an octanethiol self-assembled monolayer (SAM). Thiol place-exchange with thymine-functionalized alkanethiol 5 then provided the derivatized colloid Thy-Au (Figure 2). To provide a control system which cannot participate in hydrogen bonding, the highly analogous MeThy-Au was prepared in a similar fashion. H
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Figure 1. Recognition motif and polymer mortar . a) Diaminotriazine-thymine recognition b) Triazine-functionalized random copolymer 1. C1.3.1
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Figure 2. Preparation of Thy-Au and MeThy-Au. Addition of polymer 1 to concentrated solutions of Thy-Au in non-competitive solvents such as dichloromethane and chloroform resulted in rapid formation of a black solid. In contrast, no precipitation was observed upon addition of 1 to the control colloid MeThy-Au. The lack of aggregation observed in the control system demonstrates that the precipitation observed upon the addition of 1 to Thy-Au was the result of specific hy
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