No abstract

This paper presents the synthesis and properties of 1,3,5‐benzenetrisamides with a particular focus on structure‐efficiency relationships of nucleation and optical property enhancement of isotactic poly(propylene) (i‐PP). A family of twenty 1,3,5‐benzenetrisamide derivatives was synthesized, in which the direction of the amide linkage between the core and the peripheral substituents, as well as their length (C‐3 to C‐6) and flexibility were systematically varied. Dissolution‐ and recrystallization temperatures of the additives in the polymer melt, the crystallization temperature of i‐PP, and the optical properties clarity and haze were determined in the additive concentration range from 200 to 2 500 ppm. Within the reported series of compounds, few exhibited very good nucleating and clarification abilities, only one with outstanding characteristics, whereas other, very closely related derivatives were found to be incapable to nucleate or clarify i‐PP, although, intriguingly, most are structural isomers. We conclude that it is the particular chemical structure of the additive that determines its crystallization/self‐assembly process, and, therewith, the structure of the heterogeneous nuclei, and at a higher hierarchical level the morphology of the poly(propylene) solid state and its final properties; and, hence, that a predictive understanding is still elusive.magnified image

In this Letter, we investigate the nanomechanical properties of self-assembled 1,3,5-benzenetrisamide whiskers with atomic force microscopy (AFM) bending experiments. We use force mapping to acquire spatially resolved force measurements over the full length of a whisker segment spanning a channel of a structured glass substrate. This allows validation of the experimental boundary conditions directly from the AFM data and a reliable determination of Young's modulus. The presented technique can be generalized for the mechanical characterization of other one-dimensional materials.

No abstract

The influence of molecular structure on the mechanical properties of self-assembled 1,3,5-benzenetrisamide nanofibers is investigated. Three compounds with different amide connectivity and different alkyl substituents are compared. All the trisamides form well-defined fibers and exhibit significant differences in diameters of up to one order of magnitude. Using nanomechanical bending experiments, the rigidity of the nanofibers shows a difference of up to three orders of magnitude. Calculation of Young's modulus reveals that these differences are a size effect and that the moduli of all systems are similar and in the lower GPa range. This demonstrates that variation of the molecular structure allows changing of the fibers' morphology, whereas it has a minor influence on their modulus. Consequently, the stiffness of the self-assembled nanofibers can be tuned over a wide range--a crucial property for applications as versatile nano- and micromechanical components.