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The fabrication of ultrathin films that are electrically conductive and mechanically strong for electromagnetic interference (EMI) shielding applications is challenging. Herein, ultrathin, strong, and highly flexible Ti3C2T x MXene/bacterial cellulose (BC) composite films are fabricated by a scalable in situ biosynthesis method. The Ti3C2T x MXene nanosheets are uniformly dispersed in the three-dimensional BC network to form a mechanically entangled structure that endows the MXene/BC composite films with excellent mechanical properties (tensile strength of 297.5 MPa at 25.7 wt % Ti3C2T x ) and flexibility. Importantly, a 4 μm thick Ti3C2T x /BC composite film with 76.9 wt % Ti3C2T x content demonstrates a specific EMI shielding efficiency of 29141 dB cm2 g–1, which surpasses those of most previously reported MXene-based polymer composites with similar MXene contents and carbon-based polymer composites. Our findings show that the facile, environmentally friendly, and scalable fabrication method is a promising strategy for producing ultrathin, strong, and highly flexible EMI shielding materials such as the freestanding Ti3C2T x /BC composite films for efficient EMI shielding to address EMI problems of a fast-developing modern society.

Unlike the bewildering situation in the γγ * → π form factor, a widespread view is that perturbative QCD can decently account for the recent BaBar measurement of γγ * → ηc transition form factor. The next-to-next-to-leading order (NNLO) perturbative correction to the γγ * → η c,b form factor, is investigated in the NRQCD factorization framework for the first time. As a byproduct, we obtain by far the most precise order-α 2 s NRQCD matching coefficient for the η c,b → γγ process. After including the substantial negative order-α 2 s correction, the good agreement between NRQCD prediction and the measured γγ * → ηc form factor is completely ruined over a wide range of momentum transfer squared. This eminent discrepancy casts some doubts on the applicability of NRQCD approach to hard exclusive reactions involving charmonium.

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We compute the next-to-next-to-leading order (NNLO) QCD corrections to the hadronic decay rates of the pseudoscalar quarkonia, at the lowest order in velocity expansion. The validity of NRQCD factorization for inclusive quarkonium decay process, for the first time, is verified to relative order α 2 s . As a byproduct, the renormalization group equation (RGE) of the leading NRQCD 4-fermion operator O1( 1 S0) is also deduced to this perturbative order. By incorporating this new piece of correction together with available relativistic corrections, we find that there exists severe tension between the state-of-the-art NRQCD predictions and the measured ηc hadronic width, and in particular the branching fraction of ηc → γγ. NRQCD appears to be capable of accounting for η b hadronic decay to a satisfactory degree, and our most refined prediction is Br(η b → γγ) = (4.8 ± 0.7) × 10 −5 . Heavy quarkonium decay has historically played a preeminent role in establishing asymptotic freedom of QCD [1,2]. Due to the nonrelativistic nature of heavy quark inside a quarkonium, the decay rates are traditionally expressed as the squared bound-state wave function at the origin multiplying the short-distance quarkantiquark annihilation decay rates. With the advent of the modern effective-field-theory approach, the nonrelativistic QCD (NRQCD), this factorization picture has been put on a firmer ground, and one is allowed to systematically include the QCD radiative and relativistic corrections when tackling various quarkonium decay and production processes [3].