Introductory programming: a systematic literature review

As computing becomes a mainstream discipline embedded in the school curriculum and acts as an enabler for an increasing range of academic disciplines in higher education, the literature on introductory programming is growing. Although there have been several reviews that focus on specific aspects of introductory programming, there has been no broad overview of the literature exploring recent trends across the breadth of introductory programming. This paper is the report of an ITiCSE working group that conducted a systematic review in order to gain an overview of the introductory programming literature. Partitioning the literature into papers addressing the student, teaching, the curriculum, and assessment, we explore trends, highlight advances in knowledge over the past 15 years, and indicate possible directions for future research

Interfacial Roughening Induced by the Reaction of End-Functionalized Polymers at a PS/P2VP Interface: Quantitative Analysis by DSIMS

The reaction of end-functionalized polymer chains at the melt interface between the immiscible polymers, polystyrene (PS) and poly(2-vinylpyridine) (P2VP), has been investigated experimentally. Diblock copolymers were formed at the interface by the reaction of amine end-functionalized deuterated PS with anhydride end-functionalized P2VP. The normalized interfacial excess (ξ = z*PS/Rg,PS) of the deuterium-labeled block copolymer was determined using dynamic secondary ion mass spectrometry (DSIMS). As ξ increases, the interfacial tension decreases to zero, at which point the interface becomes unstable, inducing interfacial roughening by hydrodynamic flow of the homopolymers. Roughening was detected using scanning force microscopy (SFM) after removing the polystyrene with a selective solvent. Evidence of the interfacial instability was also observed by cross-sectional transmission electron microscopy (TEM). The length scale of the corrugation was around 15 nm, which was comparable to the diameter of diblock copolymer emulsified droplets found near the interface. For a short symmetric block copolymer (PS (4K)−P2VP (4K)), we observed that the interfacial roughening takes place above ξ = 0.9, in good agreement with the predictions of self-consistent mean-field theory.We acknowledge the support of the UCSB Materials Research Lab. (NSF-DMR-MRSEC Grant DMR00-80034). The skillful help of Dr. Tom Mates and Dr. Krystyna Brzezinska of this facility as well as useful discussions with Dr. Ryan Hayward and Dr. Seung-Heon Lee is greatly appreciated

Surface Stability in Liquid-Crystalline Block Copolymers with Semifluorinated Monodendron Side Groups

Block copolymers with semifluorinated monodendron side groups were synthesized by attachment of a first generation 2- or 3-armed monodendron acid chloride to a hydroxylated poly(styrene-b-1,2/3,4-isoprene). A convergent growth strategy was developed to synthesize the monodendron groups in good yield using an approach that could be extended to higher generation monodendrons. High extents of attachment were achieved despite the steric effects of the bulky monodendron side groups. The resulting polymers formed a smectic B mesophase at room temperature as determined by WAXS data. The transition temperatures, mesophase range, and enthalpy of the smectic B−isotropic transition were all affected by side-group structural factors such as flexible spacer length, mesogen length, and monodendron core. The critical surface tensions of the resulting semifluorinated polymers were as low as 8 mN/m as determined by Zisman analysis. Surface stability of polymer films in a polar liquid environment was strongly dependent on the extent of attachment exhibited by the semifluorinated groups. The monodendron −CF2− helix within 1 nm of the surfaces has a net orientation normal to the surface as measured by near-edge X-ray absorption fine structure (NEXAFS) methods, but the orientational order parameter Shelix is much higher for the 2-armed monodendrons than for the 3-armed monodendrons. In both cases Shelix seems insensitive to monodendron attachment density along the isoprene block. We suggest that packing frustration of the monodendron subunits produces surfaces with spontaneous curvature that differs depending on whether the monodendrons are 2- or 3-armed. The more highly curved surface topology of the 3-armed monodendrons may provide a partial explanation for its decreased orientational order.The primary support of the Office of Naval Research (Grant N00014-95-1-0695) and partial support by National Science Foundation, Division of Materials Research, Polymers Program under Grants DMR98-03738, DMR93-21573, and DMR93-214573 are gratefully acknowledged. The work at NCSU was supported by start-up funds from NCSU and from a NSF Career Award to J.G. We also acknowledge Cornell High Energy Synchrotron Source (CHESS) and the Cornell Center for Materials Research (CCMR). NEXAFS experiments were carried out at the National Synchrotron Light Source, Brookhaven National Laboratory, which is supported by the U.S. Department of Energy, Division of Materials Sciences and Division of Chemical Sciences

Temperature Dependence of Molecular Orientation on the Surfaces of Semifluorinated Polymer Thin Films

Near-edge X-ray absorption fine structure is used to investigate the temperature dependence of molecular orientation of semifluorinated liquid crystalline (SF-LC) mesogens, which are attached to the modified isoprene backbone of (i) a poly(1,2-isoprene) homopolymer and (ii) a diblock copolymer consisting of polystyrene and poly(1,2-isoprene) blocks. Our experiments reveal the existence of two temperature regions in which the surface orientation of the SF-LC mesogens changes abruptly, but even 30 K above the highest such temperature region the surface orientation does not become isotropic. The lower temperature surface transition for both homopolymer and block copolymer occurs close to the temperature of the bulk homopolymer smectic-B to smectic-A transition and well above the bulk smectic-B to smectic-A transition in the block copolymer. It seems to be controlled exclusively by the ordering phenomena originating from the surface. In contrast, the change in the surface organization of the SF-LC mesogens at higher temperatures can be associated with the bulk LC transition from the smectic-A to the isotropic phase.This research was supported by the Office of Naval Research, Grant No. N00014-92-J-1246 and the Division of Materials Research, NSF Polymers Program, Grant DMR92-23099. Partial support from Division of Materials Research, NSF Polymer Program, Grant DMR93-214573, is also appreciated

The Orientation of Semifluorinated Alkanes Attached to Polymers at the Surface of Polymer Films

The surface molecular orientation of a liquid crystalline (LC) layer made up of semifluorinated (SF) single side groups [−CO−(CH2)x-1−(CF2)yF] (single SF groups) attached to polyisoprene homopolymer or the isoprene block of a styrene−isoprene diblock copolymer was determined by analyzing the partial electron yield C-edge NEXAFS signal. The results show that the surfaces of thin SF polymer films are covered with a uniform layer, consisting of the SF−LC groups whose average −CF2− tilt angle with the surface normal lies in the range 29−46°. This is in direct contrast to the bulk, where the directors of the SF−LC mesogens are aligned parallel to the polystyrene/SF−polyisoprene interface of the block copolymers. This average tilt angle increases with increasing the length of the −(CH2)x-1− group (x increases) but decreases with increasing the length of the −(CF2)y− part of the molecule (y increases) at constant x.This research was supported by the Office of Naval Research, Grant No. N00014-92-J-1246. Partial support from Division of Materials Research, NSF Polymer Program, Grants No. DMR92-23099 and DMR93-214573, is also appreciated. The work at NC State University was supported by the NCSU COE start-up funds and the NSF CAREER award, Grant No. DMR98-75256. The authors thank Dr. B. Glu¨ sen and Ms. S. Yang (Cornell University) for their assistance during the course of the NEXAFS experiments. K.C. greatly acknowledges the financial support from the LG-Yonam Foundation for a sabbatical visit to Cornell University (1997-1998). NEXAFS experiments were carried out at the National Synchrotron Light Source, Brookhaven National Laboratory, which is supported by the U.S. Department of Energy, Division of Materials Sciences and Division of Chemical Sciences. This work made use of MRL Central Facilities at UCSB supported by the National Science Foundation under Grant No. DMR96-32716

Molecular Orientation of Single and Two-Armed Monodendron Semifluorinated Chains on Soft and Hard Surfaces Studied Using NEXAFS

Near-edge absorption fine structure (NEXAFS) measurements are used to probe the molecular orientation of semifluorinated (SF) mesogens, −(CH2)x(CF2)yF, which are attached to (i) the isoprene backbone of polyisoprene or a styrene-isoprene diblock copolymer (soft substrate), and (ii) a Au-covered solid substrate via a thiol link (hard substrate). The SF groups on both surfaces are oriented and on average are tilted from the sample normal. The tilt angle, τF-helix, of the fluorinated part of the SF group on each substrate is determined exclusively by the combination of x and y, increasing with increasing x and with decreasing y. Moreover, τF-helix is found to be independent of the surface topology (flat surfaces vs surfaces covered with holes or islands of the copolymer), casting solvent, and the architecture of the SF group (single vs 2-armed monodendron). Comparing the orientation of the SF groups on both substrates reveals that τF-helix is approximately 14° higher on the soft substrate.This research was supported by the Office of Naval Research, Grant No. N00014-92-J-1246. Partial support from Division of Materials Research, NSF Polymer Program, Grants No. DMR92-23099 and DMR93-214573, is also appreciated. This work made use of MRL Central Facilities at UCSB supported by the National Science Foundation under award no. DMR96-32716. The work at NC State University was supported by the NCSU COE start-up funds and the NSF CAREER award, Grant No. DMR98-75256. The work at the University of Houston was supported by the National Science Foundation, Grant No. DMR97-00662. K.C. greatly acknowledges the financial support from the LG-Yonam Foundation for a sabbatical visit to Cornell University (1997-1998)