A renewed focus on the phase behavior of nominally single-component, compositionally asymmetric diblock copolymers has revealed a host of previously unanticipated Frank–Kasper (FK) and quasicrystalline phases. However, these periodic and aperiodic particle packings have thus far only been reported in low molecular weight, highly conformationally asymmetric diblock copolymers, leaving researchers with a relatively small library of polymers in which these phases can be studied. In this work, we report on a simple approach to access these morphologies: blending two diblock copolymers with the same corona block length and varied core block lengths. Compositionally symmetric and asymmetric polystyrene-b-1,4-polybutadiene (SB) diblock copolymers with constant corona block lengths were blended together and shown via small-angle X-ray scattering and transmission electron microscopy to order into the FK A15 and σ phases, as well as a dodecagonal quasicrystal, providing a route to various particle packings in high molecular weight diblock copolymer melts.

Over the past decade, a wealth of complexity has been reported in the packing of compositionally asymmetric, particle-forming diblock copolymer melts, beginning with the discovery of the Frank−Kasper σ phase and continuing with subsequent discoveries of a dodecagonal quasicrystal and the C14, C15, and A15 phases. First identified by self-consistent mean-field theory (SCFT), blending diblock copolymers has proven to be a useful strategy in extending these packings to new chemistries and length scales. However, much of the immense phase space created on blending two copolymers remains unexplored. Herein, we expand on our previous work investigating binary blends of polystyrene-block-1,4-polybutadiene diblock copolymers, focusing on binary mixtures with a constant corona (majority) block length and a range of ratios of core (minority) block lengths. Small-angle X-ray scattering and transmission electron microscopy conducted with 5 narrow dispersity diblock copolymers and the associated blends uncovered a rich phase space including 12 distinct nanostructures. Notably, in agreement with SCFT predictions, we document a C14 Laves phase at low fractions of the larger copolymer in a mixture of high and low molecular weight components. However, experiments and SCFT calculations reveal that this window is truncated by close packing when the smaller copolymer is weakly segregated. Moreover, we find that even a modest difference in core block lengths is sufficient to stabilize the σ phase, highlighting the impact of core block dispersity in previous studies as well as the utility of blending in accessing these complex particle phases.

Reanalysis of an asymmetric poly(ethylene-altpropylene)-block-polydimethylsiloxane (PEP-PDMS) diblock copolymer first investigated in 1999 has revealed a rich phase behavior including a dodecagonal quasicrystal (DDQC), a Frank−Kasper σ phase, and a body-centered cubic (BCC) packing at high temperature adjacent to the disordered state. On subjecting the sample to large amplitude oscillatory shear well below the σ-BCC order−order transition temperature (T OOT ), small-angle X-ray scattering evidenced the emergence of a twinned BCC phase that, on heating, underwent a phase transition to an unusually anisotropic DDQC state. Surprisingly, we observe no evidence of this apparent epitaxy on heating or cooling through the equilibrium σ-BCC transition. We rationalize these results in terms of a shear-induced order−order transition and an apparent BCC-DDQC epitaxy favored by micelle translation-mediated ordering dynamics far below T OOT .

N3-Ligated Ni(ii) diketonate complexes are air stable and do not exhibit oxidative cleavage within the diketonate ligand under aerobic conditions.

PurposeMoringa (Moringa oleifera) is a highly nutritious, fast-growing crop that has emerged in Western markets as a “superfood” and as a “smart crop” for income generation potential among small-scale farmers. As such, moringa has been widely promoted by agricultural development practitioners in low-income countries and by emerging businesses aimed at achieving nutritional and social impact. However, the intrinsic nutritional and agronomic strengths of moringa are not enough to warrant its widespread promotion without first evaluating its economic potential to farmers.Design/methodology/approachA Land Use System (LUS) analysis modeling tool was employed to test the economic performance of two sets of moringa production practices in Kenya. Data were collected during in-depth interviews and field visits with farmers in Meru that supply a local market, and in Shimba Hills that supply an organic export market.FindingsResults suggest that current production practices over an 12-years assessment period generate a Net Present Value (NPV) of US$8,049 [ha-1] in Meru and a negative NPV of US$697 [ha-1] in Shimba Hills; with average daily returns to family labor of these two production systems of roughly 1.6 times and 0.13 times the prevailing local wage rate, respectively. These differences were attributed to a higher farmgate prices and greater yields in Meru. The analysis tool was then used to predict the effects of changes in farming practices, e.g. if farmers in Meru switched to intensive bed cultivation NPV is estimated to increase by ∼650%.Research limitations/implicationsThis study demonstrates the importance of examining the economic performance of agricultural production systems intended to increase the benefits to small-scale farmers.Originality/valueOur study is the first to assess moringa's economic performance within two production systems in Kenya – a local farmers' cooperative in Meru, and a group of farmers contracted by an export company.