The synthesis and characterization of a family of well-defined liquid crystal−coil (LC−coil) diblock copolymers have been carried out. The block copolymers in this study have been designed to have nearly identical molecular weight azobenzene-containing LC blocks in order to eliminate possible variations in LC behavior caused by the differences in the LC block molecular weight. Quantitative hydroboration chemistry was used to convert the pendent double bonds of an isoprene block to hydroxyl groups to which the mesogenic groups were attached via acid chloride coupling. The LC homopolymer and the block copolymers (LC volume fraction from f LC = 0.82 to f LC = 0.20) all exhibited smectic mesophases with similar clearing transition temperatures. The clearing transition enthalpies strongly depend on the block composition ratio and decrease as the LC block volume fraction decreases. Solvent-casting of a lamellar LC−coil copolymer (SICN5-66/60) resulted in an oriented bulk film in which both the axes of the mesogenic groups and the lamellar interfaces lie parallel to the film surfaces. A LC cylinder morphology was observed with a f LC = 0.22 LC-containing block (SICN5-176/55) using TEM and confirmed by SAXS measurements. This is the first observation with the LC block in a cylinder microdomain. Other morphologies (bicontinuous, LC sphere) were observed by TEM while retaining the smectic order in the LC microphase.

Low-stress creep measurements on a nematic liquid crystal polymer indicate that it is a viscoelastic solid, with a modulus of 100 dynes/cm 2 and a yield stress of 50 dynes/cm 2 . Both smectics and nematics are viscoelastic solids at very low stress levels, with a modulus that is related to their defect texture. At stress levels somewhat above the yield stress, there is a yielding regime where the deformation rate and defect spacing are power laws in the applied stress. We understand these power laws using the ideas developed long ago by Orowan for the motion of line defects in crystalline solids. The exponents of these power laws are different for nematics and smectics, but the nematic universality class also appears to apply to superplastic metals and ceramics.

No abstract

Progressively, the oil and gas industry is producing from unconventional reservoirs with low permeability in numerous small pay zones that require close well spacing and multiple stimulations in each well. To effectively produce from such reservoirs and reduce the surface footprint, ExxonMobil has drilled multiple wells from single pads, and new technologies have been developed to efficiently stimulate the multiple pay zones in each well. ExxonMobil has developed and licensed Multi-Zone Stimulation Technologies (MZST), which are designed to efficiently stimulate wells with multiple pays zones. The technologies have been applied in fracturing tight gas reservoirs with numerous lenticular sands in the Rocky Mountains. We have also developed a technology that enables the simultaneous stimulation of multiple wells on the same or different well pads, and while drilling additional wells. The benefits of this technology include reduced environmental impact, time saving, and improved production rates. Most importantly we have demonstrated that these simultaneous operations can be conducted in a safe and responsible manner to ensure the highest standards of operations integrity. This paper introduces the method and apparatus for this technology and discusses the results from several years of field applications, including the Piceance Basin. Some specific elements of the simultaneous operations safety plan will also be provided. Introduction Worldwide, substantial oil and gas resources are contained in low permeability formations. Many of these resources are characterized by thick intervals and/or multiple reservoir targets. In addition, matrix or fracture stimulation treatments are typically required to effectively and optimally produce these resources. However, the increased geologic and reservoir heterogeneities present in these resources can lead to substantial challenges in the stimulation treatment operations and effectiveness. Over the last several decades, industry has invested substantial research in attempts to develop new drilling and completion technologies for application in tight gas sand reservoirs. Various government and industry studies indicate a vast amount of tight gas resources exist within the United States alone, with similar resources located outside the U.S. Examples of such resources are found widely distributed in the western United States, and include the Green River, Piceance, Wind River and Uinta Basins.

Small‐angle neutron scattering is utilized to determine the flow induced alignment of a model thermotropic liquid crystalline polymer (LCP) as a function of shear rate and temperature. The results demonstrate that the flow‐induced structures in thermotropic liquid crystalline polymers have similarities and differences to those in lyotropic liquid crystalline polymer solutions. The shear rate dependence of the alignment shows that the flow‐induced alignment correlates very well to the viscosity behavior of the LCP in the shear thinning regime, while temperature variation results in a change in the extent of alignment within the nematic phase. Relaxation results also demonstrate that the flow‐induced alignment remains essentially unchanged for up to an hour after the shear field has been removed. Last, there exists a regime at low shear rate and low temperature where alignment of the LCP molecule perpendicular to the applied shear flow is stable. These results provide important experimental evidence of the molecular level changes that occur in a thermotropic liquid crystalline polymer during flow, which can be utilized to develop theoretical models and more efficiently process thermotropic polymers. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 3017–3023, 1998