Molecular Combing of a Flexible Polymer Chain by Simple Spin-Casting

Abstract

If polymer chains could be fixed on a substrate as a fully elongated chain, a procedure known as “ molecular combing ”, the chain structure could be analyzed more precisely than has been possible with the characterization techniques available today. Although the molecular combing of a rigid biomolecule, DNA, has been attained for the mapping of genetic information, that of flexible chains has never been achieved as yet. We show here that poly( n -nonyl acrylate) (PNA) can be molecularly combed on mica by a simple spin-casting method, and that the chain lengths were in good agreement with that of the all-trans conformation. One of the key factors for successful molecular combing was found to be the weak adsorption of PNA on mica, indicating that flexible polymers may be molecularly combed by adjusting their affinity to the substrate. The molecular combing of polymer chains may open a new way not only to characterize the chain structures more precisely but also to fabricate new nanomaterials based on polymers.

Molecular Combing of Various Poly(n-Alkyl Acrylate) Chains on Mica by the Dipping Method

“…As mentioned in the Introduction, we reported that the PNA chains were molecularly combed as close to the all-trans conformation by spin-casting a chloroform solution on mica . We first explored the conditions under which molecular combing was attained by the dipping method using PNA and found that the PNA chains could be molecularly combed by the dipping method under optimized conditions.…”

“…Chloroform is a good solvent for all the polymers studied here. In the chloroform solution, with an increase in the length of the alkyl group in the side chain, the polymer chains moderately expand due to steric hindrance between the long side alkyl chains, but the expansion ratio is rather moderate and still leads to random coils [see Sections 3–6 in ref ]. It is rational to think that the molecular combing occurred during the dipping process.…”

“…As mentioned in the Introduction, we reported that the PNA chains were molecularly combed as close to the all-trans conformation by spin-casting a chloroform solution on mica. 26 We first explored the conditions under which molecular combing was attained by the dipping method using PNA and found that the PNA chains could be molecularly combed by the dipping method under optimized conditions. However, as will be described later, the molecular combing strongly depended on various conditions, such as the dip speed, temperature of the dipping solution, method of drying and fixing the dipped chains by passing nitrogen over the dipped mica surface, and humidity during dipping.…”

“…The concentration of the dipping solution was 1.0 × 10 −6 g/mL, which was one order of magnitude more dilute than the concentration previously used for the molecular combing of the same PNA by the spin-casting method. 26 In the spin cast method, one drop of polymer solution was dropped onto rotating mica and was immediately blown off the substrate, whereas in the dipping method, the substrate was immersed in the solution for a longer time, and the molecules were allowed to adsorb on mica for a sufficient length of time. The dipped chains had uniform thickness and width, and the concentration of the dipping solution was dilute enough, indicating that the PNA single chains were combed.…”

“…During direct observation of various synthetic polymers spin-cast on mica with AFM, we found that poly(n-nonyl acrylate) (PNA) chains were molecularly combed on mica to almost the all-trans conformation by spin-casting. 26 It is interesting that the PNA chain, which is a random coil in a good solvent, is fully extended on the substrate after combing by a simple spin-casting method. The direction of molecular combing on the substrate is random.…”