  Particles trapped in the evanescent field of an ultrathin optical fibre
inter-act over very long distances via multiple scattering of the fibre-guided
fields. In ultrathin fibres that support higher order modes, these
interac-tions are stronger and exhibit qualitatively new behaviour due to the
cou-pling of different fibre modes, which have different propagation
wave-vectors, by the particles. Here, we study one dimensional longitudinal
opti-cal binding interactions of chains of 3 {\mu}m polystyrene spheres under
the influence of the evanescent fields of a two-mode microfibre. The
observa-tion of long-range interactions, self-ordering and speed variation of
parti-cle chains reveals strong optical binding effects between the particles
that can be modelled well by a tritter scattering-matrix approach. The optical
forces, optical binding interactions and the velocity of bounded particle
chains are calculated using this method. Results show good agreement with
finite element numerical simulations. Experimental data and theoreti-cal
analysis show that higher order modes in a microfibre offer a promis-ing method
to not only obtain stable, multiple particle trapping or faster particle
propulsion speeds, but that they also allow for better control over each
individual trapped object in particle ensembles near the microfibre surface.
